defconfig: Enable optimize for size

The default y for this option was removed between .38 and 3.0, so
to maintain the old defconfigs, explicitly enable this config.

On an 8960 build this saves a good amount of space:

$ size kobj/vmlinux.orig kobj/vmlinux.new
   text    data     bss     dec     hex filename
   9818636  711896 1841880 12372412 bcc9bc kobj/vmlinux.orig
   8765356  711320 1841784 11318460 acb4bc kobj/vmlinux.new

Change-Id: I53b04768834fad33dc6625ec79f3de61fac96516
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
12 files changed