clk: add PowerPC corenet clock driver support

This adds the clock driver for Freescale PowerPC corenet
series SoCs using common clock infrastructure.

Signed-off-by: Tang Yuantian <Yuantian.Tang@freescale.com>
Signed-off-by: Li Yang <leoli@freescale.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>