drm/radeon: Fix NULL dereference when updating memory stats

radeon_ttm_bo_destroy() is attempting to access the resource object to
update memory counters. However, the resource object is already freed when
ttm calls this function via the destroy callback. This causes an oops when
a bo is freed:

	BUG: kernel NULL pointer dereference, address: 0000000000000010
	RIP: 0010:radeon_ttm_bo_destroy+0x2c/0x100 [radeon]
	Call Trace:
	 radeon_bo_unref+0x1a/0x30 [radeon]
	 radeon_gem_object_free+0x33/0x50 [radeon]
	 drm_gem_object_release_handle+0x69/0x70 [drm]
	 drm_gem_handle_delete+0x62/0xa0 [drm]
	 ? drm_mode_destroy_dumb+0x40/0x40 [drm]
	 drm_ioctl_kernel+0xb2/0xf0 [drm]
	 drm_ioctl+0x30a/0x3c0 [drm]
	 ? drm_mode_destroy_dumb+0x40/0x40 [drm]
	 radeon_drm_ioctl+0x49/0x80 [radeon]
	 __x64_sys_ioctl+0x8e/0xd0

Avoid the issue by updating the counters in the delete_mem_notify callback
instead. Also, fix memory statistic updating in radeon_bo_move() to
identify the source type correctly. The source type needs to be saved
before the move, because the moved from object may be altered by the move.

Fixes: bfa3357e

 ("drm/ttm: allocate resource object instead of embedding it v2")
Signed-off-by: Mikel Rychliski <mikel@mikelr.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210624045121.15643-1-mikel@mikelr.com