drm/radeon: Fix EEH during kexec

[ Upstream commit 6f7fe9a93e6c09bf988c5059403f5f88e17e21e6 ]

During kexec some adapters hit an EEH since they are not properly
shut down in the radeon_pci_shutdown() function. Adding
radeon_suspend_kms() fixes this issue.

Signed-off-by: KyleMahlkuch <kmahlkuc@linux.vnet.ibm.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>