drm/radeon: separate gart and vm functions

Both are complex enough on their own.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>

diff --cc drivers/gpu/drm/radeon/Makefile
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_gart.c
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_vm.c
Simple merge