drm/i915: Use ilk_lut_write*() for all ilk+ gamma modes

We could use the dsb to load the LUT in any gamma mode, not just
when using the multi-segment mode. So replace the direct mmio
on all ilk+ paths with the wrapper.

There are a few functions (ilk_load_lut_10(), ivb_load_lut_10())
that would never be used on a platform with dsb so we could
skip those, but probably better to keep all this 100% consistent
to avoid people getting confused and copy pasting the wrong thing
when adding a new gamma mode.

The gmch stuff I left with direct mmio since those are fairly
distinct and shouldn't cause too much confusion. Although
I've also pondered about converting everything over to dsb
command buffers and just executing it on the CPU when the
real hw is not available. But dunno if that would actually
be a good idea or not...

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221123152638.20622-13-ville.syrjala@linux.intel.com
Reviewed-by: Uma Shankar <uma.shankar@intel.com>