drm/vc4: Fix YUV plane handling when planes are in different buffers

commit  57d6e4ceb2d38c2f6d6b83f0ff719b87bb141a16 from
https://github.com/raspberrypi/linux.git

 rpi-6.1.y

YUV images can either be presented as one allocation with offsets
for the different planes, or multiple allocations with 0 offsets.

The driver only ever calls drm_fb_[dma|cma]_get_gem_obj with plane
index 0, therefore any application using the second approach was
incorrectly rendered.

Correctly determine the address for each plane, removing the
assumption that the base address is the same for each.

Fixes: fc04023f ("drm/vc4: Add support for YUV planes.")
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Meng Li <Meng.Li@windriver.com>