[astro][display] Add VPP, VPU and OSD functionality

With this change, Astro display driver is completely independent of
u-boot display initialization.

The OSD driver is still very rigid. Next step will include writing
a proper OSD driver with its own protocol that could be used by all
AmLogic platforms that use the OSD channel.

The VPU related code contains lots of magic and hardcoded values from
U-Boot due to lack of documentation.

Test: Tested on Astro EVT and P2. Also tested over netboot. Also tested
using various flavors of U-Boot with display initialization ranging from
0 display support to 100% support to make sure what we do on Astro is
truly independent of U-Boot.

Change-Id: Ia02c422bcb462de2774774b6f3c9c6a1661d92bf

[gpio] Refactor the GPIO protocol

This is a first step in a move toward using protocols to represent
individual resources. A similar change will be made to the I2C protocol
to bring it in line with how I2C is used on x86 platforms.

From the client's point of view, an instance of the ZX_PROTOCOL_GPIO
protocol now represents a single pin. The protocol remains the same,
except the "uint32_t index" has been removed from all the protocol functions.

For devices that have only one GPIO resource assigned to them, the driver
can simply call device_get_protocol() to access the GPIO protocol for the pin.
To for devices with more than one GPIO pins, a new API in the platform bus called
pdev_get_protocol() must be used instead.

In addition, we add a new protocol ZX_PROTOCOL_GPIO_IMPL, which is now
implemented by the GPIO drivers. This protocol is essentially the same as
the old GPIO protocol, except "index" has been renamed "pin".
Board drivers may use this protocol directly when doing low level system
configuration, specifying pin numbers directly.

TEST: Booted on VIM2 and Hikey.
On VIM2, USB, display, ethernet and the GPIO test driver are working properly
On Hikey, the system boots and USB is functional.

Change-Id: I44f1bc11ad9793543361a2d19d7a2de4458c334b

[astro-display] Remove overly aggressive debug assertion

Specifying 0 display configurations and a null config pointer is valid,
but this code was asserting that the config pointer was non-null even
when no configs were applied.

Test: manual
Change-Id: I9b5a111b3f135a871cd521b3f0447771b501af8f

[astro][display] Convert astro display driver to cpp

Test: Test on both EVT and P2 units

Change-Id: Iaf6594eebe3edc42fbb2d8f5c61881e7df32d55b