drm/i915: Move [more] GT registers to their own header file

A couple hunks didn't get applied while resolving the conflicts on
commit 0d6419e9 ("drm/i915: Move GT registers to their own header
file").  Add the second half of the patch as a follow-up commit.

Fixes: 0d6419e9

 ("drm/i915: Move GT registers to their own header file")
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220127234334.4016964-6-matthew.d.roper@intel.com