clk: rockchip: add pll_wait_lock for pll_enable

If pll is power down,when power up pll need wait pll lock.
The reference documents section:
	PLL frequency change and lock check

Signed-off-by: Elaine Zhang <zhangqing@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>