kbuild: beautify the log of config whitelist check

Use the kbuild style log.

Prior to this commit:

./scripts/check-config.sh u-boot.cfg \
	./scripts/config_whitelist.txt . 1>&2

With this commit:

  CFGCHK  u-boot.cfg

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/Makefile b/Makefile
index c54fc06..0b1e8a6 100644
--- a/Makefile
+++ b/Makefile
@@ -836,6 +836,10 @@
 
 cfg: u-boot.cfg
 
+quiet_cmd_cfgcheck = CFGCHK  $2
+cmd_cfgcheck = $(srctree)/scripts/check-config.sh $2 \
+		$(srctree)/scripts/config_whitelist.txt $(srctree)
+
 all:		$(ALL-y)
 ifeq ($(CONFIG_DM_I2C_COMPAT)$(CONFIG_SANDBOX),y)
 	@echo "===================== WARNING ======================"
@@ -847,8 +851,7 @@
 	@# Check that this build does not use CONFIG options that we do not
 	@# know about unless they are in Kconfig. All the existing CONFIG
 	@# options are whitelisted, so new ones should not be added.
-	$(srctree)/scripts/check-config.sh u-boot.cfg \
-		$(srctree)/scripts/config_whitelist.txt ${srctree} 1>&2
+	$(call cmd,cfgcheck,u-boot.cfg)
 
 PHONY += dtbs
 dtbs: dts/dt.dtb