drm/i915: s/gmch_{m,n}/data_{m,n}/

Rename the gmch_* M/N members to data_* to match the register
definitions and thus make life a little less confusing.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220127093303.17309-4-ville.syrjala@linux.intel.com


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