arm: mmp: Make use of the DT supported clock

Change the dtsi and dts file, soc initialization code to make
use of DT support clock.
So now in the code we do only need call of_clk_init to initialize
the clocks.

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>