Split CONFIG_CC_OPTIMIZE_FOR_SIZE into two configs

This adds a separate CONFIG_CC_OPTIMIZE_FOR_SPEED option in a choice,
in preparation for adding another optimization option. Also convert SH's
makefile to use this new option.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/Makefile b/Makefile
index 06572ac..c04b58d 100644
--- a/Makefile
+++ b/Makefile
@@ -683,7 +683,9 @@
 
 ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
 KBUILD_CFLAGS	+= -Os
-else
+endif
+
+ifdef CONFIG_CC_OPTIMIZE_FOR_SPEED
 KBUILD_CFLAGS	+= -O2
 endif