Blackfin: tweak embedded LDR env config option

Use the common config option for extracting the environment for embedding
into LDR files and clarify the LDR-specific option.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/Makefile b/Makefile
index 1abe64a..b7bf110 100644
--- a/Makefile
+++ b/Makefile
@@ -308,7 +308,7 @@
 		$(OBJCOPY) ${OBJCFLAGS} -O binary $< $@
 
 $(obj)u-boot.ldr:	$(obj)u-boot
-		$(obj)tools/envcrc --binary > $(obj)env-ldr.o
+		$(CREATE_LDR_ENV)
 		$(LDR) -T $(CONFIG_BFIN_CPU) -c $@ $< $(LDR_FLAGS)
 
 $(obj)u-boot.ldr.hex:	$(obj)u-boot.ldr