Android.mk: Use TARGET_QCOM_MEDIA_VARIANT
Fix includes for universal display HAL support

Signed-off-by: Sultanxda <sultanxda@gmail.com>
vdec: Fix compilation with display-caf

GRALLOC_USAGE_PRIVATE_CP_BUFFER is a remnant of genlock, which is deprecated in Android 4.2+ and can be removed from all display HALs.

Signed-off-by: Sultanxda <sultanxda@gmail.com>