drm/amdgpu: add fw release for sdma v5_0

commit edfaf6fa73f15568d4337f208b2333f647c35810 upstream.

sdma fw isn't released when module exit

Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Wenhui Sheng <Wenhui.Sheng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>