drm/radeon: fix incorrrect SPDX-License-Identifiers

radeon is MIT.  This were incorrectly changed in
commit b2441318 ("License cleanup: add SPDX GPL-2.0 license identifier to files with no license")
and
commit d198b34f (".gitignore: add SPDX License Identifier")
and:
commit ec8f24b7 ("treewide: Add SPDX license identifier - Makefile/Kconfig")

Fixes: d198b34f (".gitignore: add SPDX License Identifier")
Fixes: ec8f24b7 ("treewide: Add SPDX license identifier - Makefile/Kconfig")
Fixes: b2441318 ("License cleanup: add SPDX GPL-2.0 license identifier to files with no license")
Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/2053Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/.gitignore

-# SPDX-License-Identifier: GPL-2.0-only
+# SPDX-License-Identifier: MIT
 mkregtable
 *_reg_safe.h
 

drivers/gpu/drm/radeon/Kconfig

-# SPDX-License-Identifier: GPL-2.0-only
+# SPDX-License-Identifier: MIT
 config DRM_RADEON_USERPTR
 	bool "Always enable userptr support"
 	depends on DRM_RADEON

drivers/gpu/drm/radeon/Makefile

-# SPDX-License-Identifier: GPL-2.0
+# SPDX-License-Identifier: MIT
 #
 # Makefile for the drm device driver.  This driver provides support for the
 # Direct Rendering Infrastructure (DRI) in XFree86 4.1.0 and higher.