clk: s2mps11: Add support for s2mps11

This patch adds support to register three(AP/CP/BT) buffered 32.768 KHz
outputs of mfd-s2mps11 with common clock framework.

Signed-off-by: Yadwinder Singh Brar <yadi.brar@samsung.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>