As of this commit, it's guaranteed that if an object is in VRAM that its
GPU virtual address will be constant.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Fix running of destroy_context() when create_context() has never been
called for the channel, and fill in engine's tlb_flush() function pointer.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>