test: add gem_write_read_ring_switch

This is meant to exercise the bug fixed in

https://patchwork.kernel.org/patch/2825192/

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/tests/Makefile.am b/tests/Makefile.am
index a422899..c78f2d1 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -33,6 +33,7 @@
 	gem_set_tiling_vs_blt \
 	gem_tiled_blits \
 	gem_tiled_partial_pwrite_pread \
+	gem_write_read_ring_switch \
 	$(NOUVEAU_TESTS_M) \
 	kms_flip \
 	kms_render \