crocus: Set MOCS on NULL stream output buffers
We'd like to add safeguards against accidental use of MOCS 0 (uncached),
which can have large performance implications. One case where we use
MOCS of 0 is disabled stream output targets, MOCS shouldn't matter, as
there's no actual buffer to be cached.
That said, it should be harmless to set MOCS for these null stream
output buffers; we can just assume a MOCS for generic internal buffers.
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13480>