cam: drm: Add support for test-only commits

Test-only commits are used to test a commit without applying any
modification to the device. This will be used by the KMS sink to test
feature support.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Eric Curtin <ecurtin@redhat.com>
Tested-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/cam/drm.cpp

@@ -377,6 +377,8 @@ int AtomicRequest::commit(unsigned int flags)
 		drmFlags |= DRM_MODE_ATOMIC_ALLOW_MODESET;
 	if (flags & FlagAsync)
 		drmFlags |= DRM_MODE_PAGE_FLIP_EVENT | DRM_MODE_ATOMIC_NONBLOCK;
+	if (flags & FlagTestOnly)
+		drmFlags |= DRM_MODE_ATOMIC_TEST_ONLY;
 
 	return drmModeAtomicCommit(dev_->fd(), request_, drmFlags, this);
 }