r600g: only set depth bit for hw accessible depth buffers.

r600g: only set depth bit for hw accessible depth buffers.

If we get a sw accessible buffer like the S8 texture we end up
doing depth tracking on it when there is no need since we won't
ever bind it to the hardware. This leads to a sw fallback in the
transfer destruction which leads to and endless recusion loop
of fail in transfer destroy.

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