[ddk] Rename ZX_PROTOCOL_CANVAS to ZX_PROTOCOL_AMLOGIC_CANVAS

To make it clear that this is an SOC-specific protocol

TEST: boot on VIM2
Change-Id: I0b6c785f77980524d5921fb2a2feda1a8984f8ce

[dev][platform-bus] Clean-up and simplify platform bus protocol:

- Remove "flags" parameter from pbus_device_add().
Now platform devices can only be started in new devhosts.

- Add new API pbus_protocol_device_add(), for binding drivers that implement
platform bus protocols like GPIO and I2C_IMPL.
pbus_protocol_device_add() is equivalent to pbus_device_add(PDEV_ADD_PBUS_DEVHOST)
followed by pbus_wait_protocol().

- Remove pbus_wait_protocol(). pbus_protocol_device_add() does the wait for you automatically.

- Rename pbus_set_protocol() to pbus_register_protocol()

These changes will hopefully make the platform bus protocol easier
to understand and use.
I found two places where people accidentally using PDEV_ADD_PBUS_DEVHOST
inappropriately (probably copy & paste errors), which resulted in
the entire network stack and storage stack running in the platform bus devhost.
Hopefully this change will make it impossible for mistakes like that to happen again.

While doing this I also noticed that the gauss nand driver and vim2 ethernet driver
were running in the platform bus devhost. This change fixes that.

Also removed some remnants of the pbus_device_enable() API, which has been removed previously.

TEST: boot up on qemu, VIM2, gauss and astro and verified platform devices all start up properly

Change-Id: I580269bc6f53a63348ba8ab580259b1ba56dd393

[amlogic][canvas] Add canvas driver for AMLOGIC

- Added a canvas protocol
- Modified the VIM2 display driver to use the canvas
protocol instead of local canvas driver
- Removed local vim2 canvas driver

ZX-2154 #done

Test: Boot up on VIM2 board with HDMI monitor attached
Change-Id: I9e2328513fafecd1a440985f84ee41fce0c35ab9