drm/radeon: Always flush VM again on < CIK

Not doing this causes piglit hangs[0] on my Cape Verde card. No issues on
Bonaire and Kaveri though.

[0] Same symptoms as those fixed on CIK by 'drm/radeon: set VM base addr
using the PFP v2'.
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_vm.c

@@ -238,7 +238,9 @@ void radeon_vm_flush(struct radeon_device *rdev,
 	uint64_t pd_addr = radeon_bo_gpu_offset(vm->page_directory);
 
 	/* if we can't remember our last VM flush then flush now! */
-	if (!vm->last_flush || pd_addr != vm->pd_gpu_addr) {
+	/* XXX figure out why we have to flush all the time before CIK */
+	if (rdev->family < CHIP_BONAIRE ||
+	    !vm->last_flush || pd_addr != vm->pd_gpu_addr) {
 		trace_radeon_vm_flush(pd_addr, ring, vm->id);
 		vm->pd_gpu_addr = pd_addr;
 		radeon_ring_vm_flush(rdev, ring, vm);