drm: Allow CAP_PRIME on !MODESET

vgem (and our igt tests using vgem) need this. I suspect etnaviv will
fare similarly.

v2. Make it build. Oops.

Fixes: d5264ed3 ("drm: Return -ENOTSUPP when called for KMS cap with a non-KMS driver")
Cc: Michel Dänzer <michel.daenzer@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161207144939.22756-1-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_ioctl.c

@@ -230,10 +230,15 @@ static int drm_getcap(struct drm_device *dev, void *data, struct drm_file *file_
 
 	req->value = 0;
 
-	/* Only one cap makes sense with a UMS driver: */
-	if (req->capability == DRM_CAP_TIMESTAMP_MONOTONIC) {
+	/* Only some caps make sense with UMS/render-only drivers. */
+	switch (req->capability) {
+	case DRM_CAP_TIMESTAMP_MONOTONIC:
 		req->value = drm_timestamp_monotonic;
 		return 0;
+	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;
+		return 0;
 	}
 
 	/* Other caps only work with KMS drivers */
@@ -254,10 +259,6 @@ static int drm_getcap(struct drm_device *dev, void *data, struct drm_file *file_
 	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;
 	case DRM_CAP_ASYNC_PAGE_FLIP:
 		req->value = dev->mode_config.async_page_flip;
 		break;