nouveau: add an ioctl to report vram usage

This reports the currently used vram allocations.

userspace using this has been proposed for nvk, but
it's a rather trivial uapi addition.

Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

include/uapi/drm/nouveau_drm.h

@@ -61,6 +61,13 @@ extern "C" {
  */
 #define NOUVEAU_GETPARAM_VRAM_BAR_SIZE 18
 
+/*
+ * NOUVEAU_GETPARAM_VRAM_USED
+ *
+ * Get remaining VRAM size.
+ */
+#define NOUVEAU_GETPARAM_VRAM_USED 19
+
 struct drm_nouveau_getparam {
 	__u64 param;
 	__u64 value;