st: add support for INTEL_blackhole_render

st: add support for INTEL_blackhole_render

Adding a new CSO proved to be fairly difficult especially because this
extension affect draw/dispatch/blit alike.

Instead this change passes the state of the noop into the entry points
emitting the operations affected.

v2: Fix assert in default pipe caps

v3: Drop whitespace changes (Ken)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/2964>