clk: mmp: move definiton of mmp_clk_frac to clk.h

Move the definition of structure of mmp_clk_frac to
clk.h.
So device tree support can use this structure.

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>