drm: Add a SET_CLIENT_CAP ioctl

This ioctl can be used to turn some knobs in a DRM driver. The client
can ask the DRM core for an alternate view of the reality: it can be
useful to be able to instruct the core that the DRM client can handle
new functionnality that would otherwise break current ABI.

v2: Rename to ioctl from SET_CAP to SET_CLIENT_CAP (Chris Wilson)

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index 07247e2..15da412 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -303,6 +303,15 @@
 }
 
 /**
+ * Set device/driver capabilities
+ */
+int
+drm_setclientcap(struct drm_device *dev, void *data, struct drm_file *file_priv)
+{
+	return -EINVAL;
+}
+
+/**
  * Setversion ioctl.
  *
  * \param inode device inode.