drm/i915: Standardize auto-increment LUT load procedure

drm/i915: Standardize auto-increment LUT load procedure

Various gamma units on various platforms have some problems loading
the LUT index and auto-increment bit at the same time. We have to
do this in two steps. The first known case was the glk degamma LUT,
but at least ADL has another known case.

We're not going to suffer too badly from a couple of extra register
writes here, so let's just standardize on this practice for all
auto-increment LUT loads/reads. This way we never have to worry about
this specific issue again. And for good measure always reset the
index back to zero at the end (we already did this in a few places).

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221123152638.20622-6-ville.syrjala@linux.intel.com
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>