drm/vc4: plane: Keep fractional source coords inside state

Fractional source co-ordinates can be used to setup the scaling
filters, so retain the information.

Signed-off-by: Dom Cobley <popcornmix@gmail.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240621152055.4180873-2-dave.stevenson@raspberrypi.com


Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>