drm/i915/gt: Create gt/gtN/.defaults/ for per gt sysfs defaults

Create a gt/gtN/.defaults/ directory (similar to
engine/<engine-name>/.defaults/) to expose default parameter values for
each gt in sysfs. This allows userspace to restore default parameter values
after they have changed. The empty 'struct gt_defaults' will be populated
by subsequent patches.

v2: Changed 'struct intel_rps_defaults rps_defaults' to
    'struct gt_defaults defaults' (Andi)

Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/be7c30d0ae58be9d8d5b8242ba00a1b2825e63ad.1658192398.git.ashutosh.dixit@intel.com

drivers/gpu/drm/i915/gt/intel_gt_sysfs.c

@@ -101,6 +101,10 @@ void intel_gt_sysfs_register(struct intel_gt *gt)
 				 gt->i915->sysfs_gt, "gt%d", gt->info.id))
 		goto exit_fail;
 
+	gt->sysfs_defaults = kobject_create_and_add(".defaults", &gt->sysfs_gt);
+	if (!gt->sysfs_defaults)
+		goto exit_fail;
+
 	intel_gt_sysfs_pm_init(gt, &gt->sysfs_gt);
 
 	return;
@@ -113,5 +117,6 @@ void intel_gt_sysfs_register(struct intel_gt *gt)
 
 void intel_gt_sysfs_unregister(struct intel_gt *gt)
 {
+	kobject_put(gt->sysfs_defaults);
 	kobject_put(&gt->sysfs_gt);
 }

drivers/gpu/drm/i915/gt/intel_gt_types.h

@@ -75,6 +75,9 @@ enum intel_submission_method {
 	INTEL_SUBMISSION_GUC,
 };
 
+struct gt_defaults {
+};
+
 struct intel_gt {
 	struct drm_i915_private *i915;
 	struct intel_uncore *uncore;
@@ -235,6 +238,10 @@ struct intel_gt {
 
 	/* gt/gtN sysfs */
 	struct kobject sysfs_gt;
+
+	/* sysfs defaults per gt */
+	struct gt_defaults defaults;
+	struct kobject *sysfs_defaults;
 };
 
 enum intel_gt_scratch_field {