sandbox: Support loading the other FDT

We need an 'other' FDT which is different from the control FDT, so we can
check that the ofnode tests correctly handle them both.

Add this to the build along with a way to read it into the sandbox state.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/dts/Makefile b/arch/sandbox/dts/Makefile
index 6cbc9bb..b6a8847 100644
--- a/arch/sandbox/dts/Makefile
+++ b/arch/sandbox/dts/Makefile
@@ -5,7 +5,7 @@
 else
 dtb-$(CONFIG_SANDBOX) += sandbox.dtb
 endif
-dtb-$(CONFIG_UT_DM) += test.dtb
+dtb-$(CONFIG_UT_DM) += test.dtb other.dtb
 dtb-$(CONFIG_CMD_EXTENSION) += overlay0.dtbo overlay1.dtbo
 
 include $(srctree)/scripts/Makefile.dts