drm/i915: Use REG_BIT() & co. for ilk+ pfit registers

Polish the ilk+ pfit registers with REG_BIT() & co., and
also take the opportunity to unify the ivb/hsw vs. not checks
in ilk_pfit_enable() and ilk_get_pfit_config().

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230418175528.13117-8-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>