Blackfin arch: extract the entry point from the linked kernel

extract the entry point from the linked kernel rather than
assuming entry point == load address
Signed-off-by: Bryan Wu <bryan.wu@analog.com>

arch/blackfin/boot/Makefile

@@ -13,7 +13,8 @@ extra-y += vmlinux.bin vmlinux.gz
 
 quiet_cmd_uimage = UIMAGE  $@
       cmd_uimage = $(CONFIG_SHELL) $(MKIMAGE) -A $(ARCH) -O linux -T kernel \
-                   -C gzip -a $(CONFIG_BOOT_LOAD) -e $(CONFIG_BOOT_LOAD) -n 'Linux-$(KERNELRELEASE)' \
+                   -C gzip -n 'Linux-$(KERNELRELEASE)' -a $(CONFIG_BOOT_LOAD) \
+                   -e $(shell $(NM) vmlinux | awk '$$NF == "__start" {print $$1}') \
                    -d $< $@
 
 $(obj)/vmlinux.bin: vmlinux FORCE