codec2: libgav1 integration part 1

This CL contains stuff that are pretty much copied over from the
libaom component. It makes it easier to review the series of CLs.

All the libgav1 specific functions will follow in a subsequent CL.

Test: all AV1 CTS tests still pass.
Bug: 131989882

Change-Id: Iaafbf5379577bd42c7de64c7ec96d5b0fbb45b18