drm/vc4_plane: Add support for YUV444 formats

Support displaying DRM_FORMAT_YUV444 and DRM_FORMAT_YVU444 formats.
Tested with kmstest and kodi. e.g.

kmstest -r 1920x1080@60 -f 400x300-YU24

Note: without the shift of width, only half the chroma is fetched,
resulting in correct left half of image and corrupt colours on right half.

The increase in width shouldn't affect fetching of Y data,
as the hardware will clamp at dest width.

Signed-off-by: Dom Cobley <popcornmix@gmail.com>