freedreno/a6xx: move ubwc clear to blitter

freedreno/a6xx: move ubwc clear to blitter

Avoid having to mmap() unnecessarily by moving UBWC clear/init to
blitter.

Because we don't have a context when the bo is allocated, we need to
lazily initialize UBWC data, so hook into the resource_written()
tracking to do this.  Don't bother with resource_read() because that
would be undefined anyways.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6475>