Makefile: add endian link flag to u-boot-elf.o

fix compile error when using a little-endian to build with configs:
	sfr_nb4-ser_ram_defconfig
	comtrend_wap5813n_ram_defconfig
	comtrend_ar5387un_ram_defconfig
	comtrend_ct5361_ram_defconfig
	comtrend_vr3032u_ram_defconfig
	comtrend_ar5315u_ram_defconfig
	huawei_hg556a_ram_defconfig
	netgear_dgnd3700v2_ram_defconfig

Signed-off-by: Du Huanpeng <dhu@hodcarrier.org>
diff --git a/Makefile b/Makefile
index 81349a7..4b347d3 100644
--- a/Makefile
+++ b/Makefile
@@ -1708,6 +1708,7 @@
 
 quiet_cmd_u-boot-elf ?= LD      $@
 	cmd_u-boot-elf ?= $(LD) u-boot-elf.o -o $@ \
+	$(if $(CONFIG_SYS_BIG_ENDIAN),-EB,-EL) \
 	-T u-boot-elf.lds --defsym=$(CONFIG_PLATFORM_ELFENTRY)=$(CONFIG_SYS_TEXT_BASE) \
 	-Ttext=$(CONFIG_SYS_TEXT_BASE)
 u-boot.elf: u-boot.bin u-boot-elf.lds