drm/vc4: hdmi: Replace CSC_CTL hardcoded value by defines

On BCM2711, the HDMI_CSC_CTL register value has been hardcoded to an
opaque value. Let's replace it with properly defined values.

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220120151625.594595-9-maxime@cerno.tech