dt: OF_UNITTEST make dependency broken

If CONFIG_OF_UNITTEST=y then a kernel image make will always cause .version to
be incremented, even if there are not source changes.  This is caused by
a lack of dependency tracking and checking for
drivers/of/unittest-data/testcases.dtb.o.
Signed-off-by: Frank Rowand <frank.rowand@sonymobile.com>
Signed-off-by: Rob Herring <robh@kernel.org>

drivers/of/Makefile

@@ -6,8 +6,7 @@ obj-$(CONFIG_OF_PROMTREE) += pdt.o
 obj-$(CONFIG_OF_ADDRESS)  += address.o
 obj-$(CONFIG_OF_IRQ)    += irq.o
 obj-$(CONFIG_OF_NET)	+= of_net.o
-obj-$(CONFIG_OF_UNITTEST) += of_unittest.o
-of_unittest-objs := unittest.o unittest-data/testcases.dtb.o
+obj-$(CONFIG_OF_UNITTEST) += unittest.o
 obj-$(CONFIG_OF_MDIO)	+= of_mdio.o
 obj-$(CONFIG_OF_PCI)	+= of_pci.o
 obj-$(CONFIG_OF_PCI_IRQ)  += of_pci_irq.o
@@ -16,5 +15,7 @@ obj-$(CONFIG_OF_RESERVED_MEM) += of_reserved_mem.o
 obj-$(CONFIG_OF_RESOLVE)  += resolver.o
 obj-$(CONFIG_OF_OVERLAY) += overlay.o
 
+obj-$(CONFIG_OF_UNITTEST) += unittest-data/
+
 CFLAGS_fdt.o = -I$(src)/../../scripts/dtc/libfdt
 CFLAGS_fdt_address.o = -I$(src)/../../scripts/dtc/libfdt

drivers/of/unittest-data/.gitignore

+testcases.dtb
+testcases.dtb.S

drivers/of/unittest-data/Makefile

+obj-y += testcases.dtb.o
+
+targets += testcases.dtb testcases.dtb.S
+
+.SECONDARY: \
+	$(obj)/testcases.dtb.S \
+	$(obj)/testcases.dtb