fwu: DeveloperBox: add support for FWU

Add code to support FWU_MULTI_BANK_UPDATE.
The platform does not have gpt-partition storage for
Banks and MetaData, rather it used SPI-NOR backed
mtd regions for the purpose.

Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
diff --git a/board/socionext/developerbox/Makefile b/board/socionext/developerbox/Makefile
index 4a46de9..1acd067 100644
--- a/board/socionext/developerbox/Makefile
+++ b/board/socionext/developerbox/Makefile
@@ -7,3 +7,4 @@
 #
 
 obj-y	:= developerbox.o
+obj-$(CONFIG_FWU_MDATA_MTD) += fwu_plat.o