arm: mmp: make all SOCs use common clock by default

Signed-off-by: Chao Xie <xiechao.mail@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>