drm/radeon: fix incorrrect SPDX-License-Identifiers

drm/radeon: fix incorrrect SPDX-License-Identifiers

radeon is MIT.  This were incorrectly changed in
commit e18caa17255e ("License cleanup: add SPDX GPL-2.0 license identifier to files with no license")
and
commit 00d3f1631a0a (".gitignore: add SPDX License Identifier")
and:
commit 097d06b8a9ee ("treewide: Add SPDX license identifier - Makefile/Kconfig")

Fixes: 00d3f1631a0a (".gitignore: add SPDX License Identifier")
Fixes: 097d06b8a9ee ("treewide: Add SPDX license identifier - Makefile/Kconfig")
Fixes: e18caa17255e ("License cleanup: add SPDX GPL-2.0 license identifier to files with no license")
Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/2053
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>