drm/i915: Simplify modifier lookup in watermark code

Replace the huge modifier lists in the watermark code with
a few calls to intel_fb.c.

Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221003111544.8007-7-ville.syrjala@linux.intel.com