drm/i915: Parametrize PFIT_PIPE

Make the PFIT_PIPE stuff less ugly via parametrization.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200212161738.28141-2-ville.syrjala@linux.intel.com


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