gallium: Add a pipe cap for whether primitive restart works for patches.

Some hardware supports primitive restart on patch primitives, and other
hardware does not.  Modern GL and ES include a query for this feature;
adding a capability bit will allow us to answer it.

As far as I know, AMD hardware does not support this feature, while
NVIDIA and Intel hardware does.  However, most Gallium drivers do not
appear to support tessellation shaders yet.  So, I've enabled it for
nvc0 and disabled it everywhere else.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/gallium/docs/source/screen.rst

@@ -338,6 +338,8 @@ The integer capabilities:
   and accesses to unbound resources.
 * ``PIPE_CAP_CULL_DISTANCE``: Whether the driver supports the arb_cull_distance
   extension and thus implements proper support for culling planes.
+* ``PIPE_CAP_PRIMITIVE_RESTART_FOR_PATCHES``: Whether primitive restart is
+  supported for patch primitives.
 
 
 .. _pipe_capf: