fdt: fix dts preprocessor options

Using "-ansi" preprocessor option will cause dts lines that begin with
'#' to choke the preprocessor.  Change to "-x assembler-with-cpp"
instead which is what the kernel uses to preprocess dts files.

Signed-off-by: Allen Martin <amartin@nvidia.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>

dts/Makefile

@@ -36,7 +36,7 @@ $(error Your architecture does not have device tree support enabled. \
 Please define CONFIG_ARCH_DEVICE_TREE))
 
 # We preprocess the device tree file provide a useful define
-DTS_CPPFLAGS := -ansi \
+DTS_CPPFLAGS := -x assembler-with-cpp \
 		-DARCH_CPU_DTS=\"$(SRCTREE)/arch/$(ARCH)/dts/$(CONFIG_ARCH_DEVICE_TREE).dtsi\" \
 		-DBOARD_DTS=\"$(SRCTREE)/board/$(VENDOR)/$(BOARD)/dts/$(DEVICE_TREE).dts\"