Add YV12 color converter interface for VideoEditor.

The original assumption in VideoEditor is that the decoder output
and encoder input are in YV12 format. However on different
hardware platform the actual formats may be different. So now we
load a platform-specific YV12 color conversion module which
knows the actual format and can convert to/from YV12, which is
the format used in VideoEditor internally for processing.

Bug: 5061733
Change-Id: I852f85efd30c05cf6c42810059ee4d2ef37ee3da