drm/i915: Use REG_BIT() & co. for pipe scaler registers

Pimp the skl+ scaler register bits with REG_BIT()/etc.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230426135019.7603-7-ville.syrjala@linux.intel.com