drm/prime: expose capability flags for userspace.

This lets the kernel tell userspace if the device supports prime
import/export.

This is useful for -modesetting at least, but would be nice for other
drivers.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_ioctl.c

@@ -283,6 +283,10 @@ int drm_getcap(struct drm_device *dev, void *data, struct drm_file *file_priv)
 	case DRM_CAP_DUMB_PREFER_SHADOW:
 		req->value = dev->mode_config.prefer_shadow;
 		break;
+	case DRM_CAP_PRIME:
+		req->value |= dev->driver->prime_fd_to_handle ? DRM_PRIME_CAP_IMPORT : 0;
+		req->value |= dev->driver->prime_handle_to_fd ? DRM_PRIME_CAP_EXPORT : 0;
+		break;
 	default:
 		return -EINVAL;
 	}