xtensa: Define PLATFORM_ELFFLAGS

u-boot.elf target requires it to work.

Tested-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>

arch/xtensa/config.mk

@@ -7,3 +7,9 @@ PLATFORM_CPPFLAGS += -D__XTENSA__ -mlongcalls -mforce-no-pic \
 		     -ffunction-sections -fdata-sections
 
 LDFLAGS_FINAL += --gc-sections
+
+ifeq ($(CONFIG_SYS_BIG_ENDIAN),y)
+PLATFORM_CPPFLAGS += -B xtensa -O elf32-xtensa-be
+else
+PLATFORM_ELFFLAGS += -B xtensa -O elf32-xtensa-le
+endif