clk: mmp: add clock type mix

The clock type mix is a kind of clock combines "div" and "mux".
This kind of clock can not allow to change div first then
mux or change mux first or div.
The reason is
1. Some clock has frequency change bit. Each time want to change
   the frequency, there are some operations based on this bit, and
   these operations are time-cost.
   Seperating div and mux change will make the process longer, and
   waste more time.
2. Seperting the div and mux may generate middle clock that the
   peripharals do not support. It may make the peripharals hang.

There are three kinds of this type of clock in all SOCes.
1. The clock has bit to trigger the frequency change.
2. Same as #1, but the operations for the bit is different
3. Do not have frequency change bit.

So this type of clock has implemented the callbacks
->determine_rate
->set_rate_and_parent
These callbacks can help to change the div and mux together.

Signed-off-by: Chao Xie <chao.xie@marvell.com>
Acked-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Signed-off-by: Michael Turquette <mturquette@linaro.org>