Zero-copy VA-API decoding using gralloc DRM prime handle

Create VA surfaces from DRM prime handle provided by gralloc. These can
then be returned by codec2 to framework with zero copy operation.

Hot-patch the ffmpeg HW accel device to inject custom frame pool
handling functions. Use C2BlockPool to generate a buffer and create a VA
surface from the DRM prime handle. Keep track of the generated buffers
based on the IGBP slot index.

Handle video resolution change (e.g. with HLS) by keeping track of the
buffer metadata and recreate the VA surface if necessary (only buffer
dimensions are expected to change).

Patching the ffmpeg HW accel device allows to be compatible with using
VA-API also for filtering (e.g. deinterlace). However all VA surfaces
must have the same dimensions, in particular for cases where frame
actual dimensions is different than the coded one. This is necessary as
one cannot control what IGBP slot will be used in what context, so all
VA surfaces must be interchangeable.

Use of DRM prime can be disabled by setting system property
debug.ffmpeg-codec2.hwaccel.drm = 0.

codec2/Android.mk

@@ -49,6 +49,9 @@ LOCAL_SHARED_LIBRARIES := \
 	libswresample \
 	libswscale \
 	libutils
+ifeq ($(CONFIG_VAAPI),yes)
+LOCAL_SHARED_LIBRARIES += libva
+endif
 include $(BUILD_EXECUTABLE)
 
 include $(CLEAR_VARS)