kconfig: add CONFIG_CC_OPTIMIZE_FOR_SIZE

Copy the Kconfig option from "init/Kconfig" of Linux v3.16 tag
and adjust the help document.
Signed-off-by: NMasahiro Yamada <yamada.m@jp.panasonic.com>

Kconfig

@@ -46,6 +46,16 @@ config LOCALVERSION_AUTO
 
 	  which is done within the script "scripts/setlocalversion".)
 
+config CC_OPTIMIZE_FOR_SIZE
+	bool "Optimize for size"
+	depends on !SPL_BUILD
+	default y
+	help
+	  Enabling this option will pass "-Os" instead of "-O2" to gcc
+	  resulting in a smaller U-Boot image.
+
+	  This option is enabled by default for U-Boot.
+
 endmenu		# General setup
 
 menu "Boot images"

Makefile

@@ -529,7 +529,11 @@ else
 include/config/auto.conf: ;
 endif # $(dot-config)
 
-KBUILD_CFLAGS += -Os #-fomit-frame-pointer
+ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
+KBUILD_CFLAGS	+= -Os
+else
+KBUILD_CFLAGS	+= -O2
+endif
 
 ifdef BUILD_TAG
 KBUILD_CFLAGS += -DBUILD_TAG='"$(BUILD_TAG)"'