drm: Put amdkfd before radeon in drm Makefile

When amdkfd and radeon are compiled inside the kernel image (not as modules),
radeon will load before amdkfd, which will cause a bug when radeon will probe
the GPUs.

When the two drivers are compiled as modules, amdkfd is loaded after radeon is
loaded but before radeon starts probing the GPUs. This is done because radeon
loads the amdkfd module through symbol_request function.

This patch makes amdkfd load before radeon when they are both compiled inside
the kernel image, which makes the behavior similar to the case when they are
modules, and prevents the kernel bug.

Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>