clk: clk-s2mps11: Refactor for including support for other MFD clocks

The clocks in S2MPS11 and S5M8767 are managed in the same way, baring
a difference in the register offset. It would be better to update
existing S2MPS11 driver to support the clocks in S5M8767, rather than
creating an almost duplicate driver altogether.

Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Reviewed-by: Yadwinder Singh Brar <yadi.brar@samsung.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>