gallium: Add MULTISAMPLE_Z_RESOLVE cap

Resolving a multisampled depth texture into
a single sampled texture is supported on >= SM4.1
hw. It is possible some previous hw support it.

The ability was tested on radeonsi and nvc0.
Apparently is is also supported for radeon >= r700.

This patch adds the MULTISAMPLE_Z_RESOLVE cap and
add it to the drivers. It is advertised for drivers
for which it is sure the ability is supported.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Axel Davy <axel.davy@ens.fr>

src/gallium/drivers/vc4/vc4_screen.c

@@ -171,6 +171,7 @@ vc4_screen_get_param(struct pipe_screen *pscreen, enum pipe_cap param)
         case PIPE_CAP_CLIP_HALFZ:
         case PIPE_CAP_VERTEXID_NOBASE:
         case PIPE_CAP_POLYGON_OFFSET_CLAMP:
+        case PIPE_CAP_MULTISAMPLE_Z_RESOLVE:
                 return 0;
 
                 /* Stream output. */