drm/i915: Prepare more multi-GT initialization

drm/i915: Prepare more multi-GT initialization

We're going to introduce an additional intel_gt for MTL's media unit
soon.  Let's provide a bit more multi-GT initialization framework in
preparation for that.  The initialization will pull the list of GTs for
a platform from the device info structure.  Although necessary for the
immediate MTL media enabling, this same framework will also be used
farther down the road when we enable remote tiles on xehpsdv and pvc.

v2:
 - Re-add missing test for !HAS_EXTRA_GT_LIST in intel_gt_probe_all().

v3:
 - Move intel_gt_definition struct to intel_gt_types.h.  (Jani)
 - Drop gtdef->setup().  For now we'll just use a switch() based on GT
   type since we don't have too many different handlers for the
   foreseeable future.  (Jani)

Cc: Aravind Iddamsetty <aravind.iddamsetty@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Reviewed-by: Aravind Iddamsetty <aravind.iddamsetty@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220906234934.3655440-6-matthew.d.roper@intel.com
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>