drm/i915: Reduce I915_MAX_GT to 2

According to Ashutosh there is no current or planned product in i915 for
I915_MAX_GT to be 4 anymore.

Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Ashutosh Dixit <ashutosh.dixit@linux.intel.com>
Cc: Andi Shyti <andy.shyti@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Signed-off-by: Matt Atwood <matthew.s.atwood@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230602231754.1596433-2-matthew.s.atwood@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -313,7 +313,7 @@ struct drm_i915_private {
 	/*
 	 * i915->gt[0] == &i915->gt0
 	 */
-#define I915_MAX_GT 4
+#define I915_MAX_GT 2
 	struct intel_gt *gt[I915_MAX_GT];
 
 	struct kobject *sysfs_gt;