v4l2_codec2: Move common code to common helpers folder.

This CL moves the C2VEAFormatConverter.cpp/h and C2VDACommon.h files to
the common helpers package, so they can be reused by the upcoming
V4L2EncodeComponent. Additionaly some fo the code in
VideoEncodeAcceleratorAdaptor.h has been moved to the common.h file.

Some files have been renamed in the process:
C2VEAFormatConverter.cpp/h -> FormatConverter.cpp/h
C2VDACommon.h -> Common.h

Note: The original C2VDACommon.h file has not been removed yet as it's
referenced by vendor/google_arc/. It will be deleted after all
references have been removed.

Bug: 143333813
Test: m -j32
Change-Id: I97044e0916518bee8882604dd68872c3f49cfafb