[dev][platform-bus] separate regular metadata from bootloader metadata

In the platform bus protocol, we use the pbus_metadata_t struct
for board drivers to pass metadata to the platform devices.
Instead of overloading this struct to work both for immediately
provided metadata and metadata passed from the bootloader, we now have
a separate struct pbus_boot_metadata_t used for specifying bootloader
metadata to be assigned to a platform device.

ZX-2513 #in progress

TEST: booted VIM2, astro and gauss and verified that drivers that
use metadata started up successfully.

Change-Id: I7065fd497646f386987cb5dc317d1c66daa8df0a

[platform-bus][aml-canvas] Add support for proxying SOC-specific protocols

This change adds support to the platform bus driver for proxying
SOC-specific protocols to platform devices without modifying the
platform bus source code. It also removes support for the Amlogic canvas
protocol from the platform bus driver and uses this new proxying support instead.

The Amlogic canvas driver is now split into two drivers:
the canvas implementation driver and the canvas proxy driver.
The implementation driver runs in the platform bus devhost and implements the main
functionality of the driver. The proxy driver runs in the devhosts of the
drivers that are clients of the canvas protocol and is responsible for proxying
the canvas protocol to the implementation driver.

To make this work we add a new protocol ZX_PROTOCOL_PLATFORM_PROXY
and add new support to ZX_PROTOCOL_PLATFORM_BUS.
In ZX_PROTOCOL_PLATFORM_BUS, the pbus_register_protocol() API now adds an
optional callback of type platform_proxy_cb_t. This callback handles
RPCs from a protocol proxy driver.

The new protocol ZX_PROTOCOL_PLATFORM_PROXY is used for protocol proxy drivers
to communicate with the platform bus in the client devhosts.
When the proxy driver loads, it calls platform_proxy_register_protocol()
to register its protocol implementation with the platform bus proxy driver.
When the client driver calls a protocol API implemented by the proxy driver,
the proxy driver calls platform_proxy_proxy() to proxy the protocol
to the implementation driver in the platform device devhost, via the channel
that connects the two devhosts.

Support for proxying the Amlogic canvas protocol is now removed from the
platform bus driver, since we are using this new mechanism instead.

Within the platform bus driver, we add a new class ProxyClient.
This is a subclass of ddk::Device that is used for binding the
protocol proxy drivers. In the case where a platform device relies on
SOC-specific protocols implemented using this new mechanism,
the platform bus proxy driver creates a PlatformProxyClient for each
of the protocols and waits for them all to register their protocols
via the ZX_PROTOCOL_PLATFORM_PROXY protocol before creating the
ProxyDevice object to bind the platform device driver.

Below illustrates the parts of the device tree is changed by this CL:

BEFORE:
[04:02:1] pid=1785 /boot/driver/platform-bus.so
<04:02:1> pid=2881 /boot/driver/platform-bus.proxy.so
[vim2-display] pid=2881 /boot/driver/vim-display.so
[display-controller] pid=2881 /boot/driver/display.so

AFTER:
[04:02:1] pid=1850 /boot/driver/platform-bus.so
<04:02:1> pid=3024 /boot/driver/platform-bus.proxy.so
[ProxyClient[7043414e]] pid=3024 /boot/driver/platform-bus.proxy.so
[aml-canvas-proxy] pid=3024 /boot/driver/aml-canvas.proxy.so
[ProxyDevice] pid=3024 /boot/driver/platform-bus.proxy.so
[vim2-display] pid=3024 /boot/driver/vim-display.so
[display-controller] pid=3024 /boot/driver/display.so

In the AFTER subtree, the platform proxy driver inserts a new root device that has
both the aml-canvas and vim2-display drivers as children.

TEST: manual testing on VIM2 and astro

Change-Id: Ibfa925948491fb3793dd934ee5737ace7903edb9

[dev][platform-bus] clang format, and remove obsolete comment

TEST: boot VIM2 successfully
Change-Id: Idc2aed5c649a929bf3baaf9ceb5c82dbaae2182e

[dev][platform-bus] Replace use of fbl::Vector with fbl::Array for some simple types

TEST: Boot on VIM2 and qemu

Change-Id: Ia64e6985491be6b015c10b447c0f8f0a1c1342af

[dev][platform-bus] Provide platform bus resources platform device children

Currently the platform bus allows creating a list of platform devices,
each running in a separate devhost.
These devices are provided by the bus with various resources
(MMIO buffers, interrupt handles, GPIOs, I2C channels, etc).
However we have use cases where a platform device may have child devices
that also need resources from the platform bus.

This change allows children of platform devices to access platform bus resources.
To do this, the board driver can pass a list of child devices via the pbus_dev_t
structure passed via pbus_device_add(). These children can also have children,
allowing for a tree of platform devices in the same devhost, rather than just one.
To facilitate this, a platform device must use a new platform device protocol
pdev_device_add() to create the child device rather than calling the DDK
device_add() directly.
The behavior of pdev_device_add() is the same as device_add(), except it inserts
a layer between the parent and child device to allow device_get_protocol()
to return protocols that are implemented by the platform bus
(for example, ZX_PROTOCOL_PLATFORM_DEV, ZX_PROTOCOL_GPIO, etc.)
This allows the children of of platform devices to also be platform devices,
while simultaneously allowing access to the protocol(s) implemented by the
parent device.

This change also adds four drivers to the qemu build to test this new functionality.
The qemu-bus board driver adds a platform device called "parent".
"parent" then creates a child device called "child-1", which in turn has
two children called "child-2" and "child-3".
All of these devices are platform devices and all four of the corresponding drivers
test to make sure that they can access the platform device protocol and map
their own unique MMIO regions.

TEST: manual testing on qemu, vim2 and gauss

Change-Id: Iaa4cd2afb06512dd0a9f9e06ca91c84c348e352f