va: videoformat: use video library to get DRM fourcc
Instead of duplicating the GStreamer format to DRM fourcc mapping, this patch uses the GstVideo library helpers. This duplicates the big O of looking for, since the two lists are traversed, but it's less error prone.
Partially reverts commit 547f3e86.
Fixes: #3354 (closed)
Cc: @He_Junyan