After the recent cleanup operations the only code left in the
VideoFrame class are helper functions directly related to the
VideoPixelFormat. This CL merges all these helpers into
video_pixel_format.h.

Additionally a helper in the VideoFrameLayout class is also moved to
the video_pixel_format.h, so all VideoPixelFormat-related helpers are
in one place.

Bug: 155138142
Test: arc.VideoEncodeAccel.h264_192p_i420_vm
Change-Id: I76699ecf69eb90fe890c1c272db058938b68062b