nv50,nvc0: serialize between before/after using a zeta surface as color

nv50,nvc0: serialize between before/after using a zeta surface as color

This happens during "3d" blit operations, where we must reinterpret it
as color in order to support stencil/depth masking. However the hardware
isn't necessarily amused by this, esp when multiple draws are queued up.
Throw in serialize calls in order to get it to flush out previous draws.

This was noticeable in the test
dEQP-GLES3.functional.fbo.invalidate.sub.unbind_blit_msaa_stencil,
although 3d blit operation had to be forced on nvc0 where it's much
rarer.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8396>