gallium/tgsi_exec: Replace the SSBO RESQ-specific interface with lookup.

gallium/tgsi_exec: Replace the SSBO RESQ-specific interface with lookup.

We've got the new lookup with size+ptr, just use that one for querying
buffer size.

This means we now return 0 instead of undefined for unbound buffers, but
it also means we return 0 for a buffer view with a size larger than that
of the underlying buffer.

Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8276>