drm/i915: Clean up DPINVGTT/VLV_DPFLIPSTAT bits

Use REG_BIT() & co. for DPINVTT/VLV_DPFLIPSTAT bits.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211112193813.8224-9-ville.syrjala@linux.intel.com


Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>