Blackfin: force BFD target when linking modules

This allows us to use any Blackfin toolchain to create kernel modules
(such as the FDPIC bfin-linux-uclibc toolchain).
Signed-off-by: NMike Frysinger <vapier@gentoo.org>

arch/blackfin/Makefile

@@ -16,6 +16,7 @@ GZFLAGS          := -9
 KBUILD_CFLAGS           += $(call cc-option,-mno-fdpic)
 KBUILD_AFLAGS           += $(call cc-option,-mno-fdpic)
 CFLAGS_MODULE    += -mlong-calls
+LDFLAGS_MODULE   += -m elf32bfin
 KALLSYMS         += --symbol-prefix=_
 
 KBUILD_DEFCONFIG := BF537-STAMP_defconfig