xtensa: define CONFIG_CPU_{BIG,LITTLE}_ENDIAN

Query compiler for the CPU endianness and add corresponding definition
to KBUILD_CPPFLAGS. This allows using 'native-endian' property in DTS.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/Makefile

@@ -53,9 +53,11 @@ endif
 
 ifeq ($(shell echo __XTENSA_EB__ | $(CC) -E - | grep -v "\#"),1)
 CHECKFLAGS += -D__XTENSA_EB__
+KBUILD_CPPFLAGS += -DCONFIG_CPU_BIG_ENDIAN
 endif
 ifeq ($(shell echo __XTENSA_EL__ | $(CC) -E - | grep -v "\#"),1)
 CHECKFLAGS += -D__XTENSA_EL__
+KBUILD_CPPFLAGS += -DCONFIG_CPU_LITTLE_ENDIAN
 endif
 
 vardirs := $(patsubst %,arch/xtensa/variants/%/,$(variant-y))