drm: move ttm global code to core drm

I wrote this for the prime sharing work, but I also noticed other external
non-upstream drivers from a large company carrying a similiar patch, so I
may as well ship it in master.

Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_drv.c

@@ -288,6 +288,7 @@ static int __init drm_core_init(void)
 {
 	int ret = -ENOMEM;
 
+	drm_global_init();
 	idr_init(&drm_minors_idr);
 
 	if (register_chrdev(DRM_MAJOR, "drm", &drm_stub_fops))