[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