drm/i915/xelpd: Enable Pipe Degamma

Enable Pipe Degamma for XE_LPD. Extend the legacy implementation
to incorparate the extended lut size for XE_LPD.

v2: Added a helper for degamma lut size (Ville)

Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211207071135.3660332-3-uma.shankar@intel.com