Blackfin: cache result of cpp check

Avoid overhead of computing this value multiple times.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

arch/blackfin/config.mk

@@ -48,9 +48,10 @@ ALL-y += $(obj)u-boot.ldr
 endif
 ifeq ($(CONFIG_ENV_IS_EMBEDDED_IN_LDR),y)
 CREATE_LDR_ENV = $(obj)tools/envcrc --binary > $(obj)env-ldr.o
-HOSTCFLAGS_NOPED += \
+HOSTCFLAGS_NOPED_ADSP := \
 	$(shell $(CPP) -dD - -mcpu=$(CONFIG_BFIN_CPU) </dev/null \
 		| awk '$$2 ~ /ADSP/ { print "-D" $$2 }')
+HOSTCFLAGS_NOPED += $(HOSTCFLAGS_NOPED_ADSP)
 else
 CREATE_LDR_ENV =
 endif