freedreno/a6xx: Move UBWC demotion to first sampler view bind

freedreno/a6xx: Move UBWC demotion to first sampler view bind

With threaded_context, CSO creation happens in the frontend thread,
which means it is no longer safe to do blits (if needed, for sampler
views with format that cannot be UBWC).  So move this to the first
time that the sampler view is bound.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9323>