video: test: Test partial updates of hardware frame buffer

video: test: Test partial updates of hardware frame buffer

With VIDEO_COPY enabled, only the modified parts of the frame buffer are
intended to be copied to the hardware. Add a test that checks this, by
overwriting contents we prepared without telling the video uclass and
then checking if the overwritten contents have been redrawn on the next
sync.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Link: https://lore.kernel.org/u-boot/20230821135111.3558478-4-alpernebiyasak@gmail.com/