drm/i915: Clean up cursor registers

Use REG_BIT() & co. to polish the cursor plane registers.

v2: deal with gvt

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211201152552.7821-12-ville.syrjala@linux.intel.com


Reviewed-by: José Roberto de Souza <jose.souza@intel.com>