winsys: return null for DONTBLOCK flag on existing winsys

Add code so that existing driver behaviour doesn't change.

src/gallium/winsys/drm/intel/gem/intel_be_device.c

@@ -26,6 +26,12 @@ intel_be_buffer_map(struct pipe_winsys *winsys,
 	int write = 0;
 	int ret;
 
+        if (flags & PIPE_BUFFER_USAGE_DONTBLOCK) {
+           /* Remove this when drm_intel_bo_map supports DONTBLOCK 
+            */
+           return NULL;
+        }
+
 	if (flags & PIPE_BUFFER_USAGE_CPU_WRITE)
 		write = 1;
 

src/gallium/winsys/drm/nouveau/common/nouveau_winsys_pipe.c

@@ -119,6 +119,12 @@ nouveau_pipe_bo_map(struct pipe_winsys *pws, struct pipe_buffer *buf,
 	struct nouveau_pipe_buffer *nvbuf = nouveau_pipe_buffer(buf);
 	uint32_t map_flags = 0;
 
+        if (flags & PIPE_BUFFER_USAGE_DONTBLOCK) {
+           /* Remove this when this code is modified to support DONTBLOCK 
+            */
+           return NULL;
+        }
+
 	if (flags & PIPE_BUFFER_USAGE_CPU_READ)
 		map_flags |= NOUVEAU_BO_RD;
 	if (flags & PIPE_BUFFER_USAGE_CPU_WRITE)

src/gallium/winsys/drm/radeon/radeon_buffer.c

@@ -112,6 +112,12 @@ static void *radeon_buffer_map(struct pipe_winsys *ws,
     struct radeon_pipe_buffer *radeon_buffer = (struct radeon_pipe_buffer*)buffer;
     int write = 0;
 
+    if (flags & PIPE_BUFFER_USAGE_DONTBLOCK) {
+       /* Remove this when radeon_bo_map supports DONTBLOCK 
+        */
+       return NULL;
+    }
+
     if (flags & PIPE_BUFFER_USAGE_CPU_WRITE) {
         write = 1;
     }