uboot: support -b option for mkenvimage

When generating the environment image the target endianess should
be taken in account for CRC calculation purposes. For big endian
targets the -b flag should be passed to the mkenvimage tool.

Signed-off-by: Tiago Brusamarello <tiago.brusamarello@datacom.ind.br>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

boot/uboot/uboot.mk

@@ -223,6 +223,7 @@ define UBOOT_INSTALL_IMAGES_CMDS
 		cat $(call qstrip,$(BR2_TARGET_UBOOT_ENVIMAGE_SOURCE)) | \
 			$(HOST_DIR)/usr/bin/mkenvimage -s $(BR2_TARGET_UBOOT_ENVIMAGE_SIZE) \
 			$(if $(BR2_TARGET_UBOOT_ENVIMAGE_REDUNDANT),-r) \
+			$(if $(filter BIG,$(BR2_ENDIAN)),-b) \
 			-o $(BINARIES_DIR)/uboot-env.bin -)
 endef