drm/i915: Add a label for config DRM_I915_SPIN_REQUEST

If we don't give it a label, it does not appear as a configuration
option.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190612093111.11684-9-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/Kconfig.profile

@@ -13,7 +13,7 @@ config DRM_I915_USERFAULT_AUTOSUSPEND
 	  runtime pm autosuspend delay tunable.
 
 config DRM_I915_SPIN_REQUEST
-	int
+	int "Busywait for request completion (us)"
 	default 5 # microseconds
 	help
 	  Before sleeping waiting for a request (GPU operation) to complete,