clk: rockchip: add pclk_pmu as critical clock on rk3128

pclk_pmu need always on, and no dts node to handle this clk,
so make it as critical clock

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