dma-buf: Exercise dma-fence-chain under selftests

A few very simple testcases to exercise the dma-fence-chain API.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Venkata Sandeep Dhanalakota <venkata.s.dhanalakota@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200409110101.18400-3-chris@chris-wilson.co.uk

drivers/dma-buf/Makefile

@@ -9,6 +9,7 @@ obj-$(CONFIG_UDMABUF)		+= udmabuf.o
 
 dmabuf_selftests-y := \
 	selftest.o \
-	st-dma-fence.o
+	st-dma-fence.o \
+	st-dma-fence-chain.o
 
 obj-$(CONFIG_DMABUF_SELFTESTS)	+= dmabuf_selftests.o

drivers/dma-buf/selftests.h

@@ -11,3 +11,4 @@
  */
 selftest(sanitycheck, __sanitycheck__) /* keep first (igt selfcheck) */
 selftest(dma_fence, dma_fence)
+selftest(dma_fence_chain, dma_fence_chain)