drm/xe: Add missing SPDX license identifiers

Ensure all Xe driver files have a proper SPDX license identifier, add it
in files where it was missing.

Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Signed-off-by: Francois Dugast <[e-mail]>
Reviewed-by: Lucas De Marchi <[e-mail]>

drivers/gpu/drm/xe/Kconfig.profile

···
+# SPDX-License-Identifier: GPL-2.0-only
 config DRM_XE_JOB_TIMEOUT_MAX
 	int "Default max job timeout (ms)"
 	default 10000 # milliseconds

drivers/gpu/drm/xe/compat-i915-headers/gem/i915_gem_stolen.h

···
+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright © 2024 Intel Corporation
+ */
+
 #ifndef _I915_GEM_STOLEN_H_
 #define _I915_GEM_STOLEN_H_