clk: sprd: add gate for pll clocks

Some sprd's gate clocks are used to the switch of pll, which
need to wait a certain time for stable after being enabled.

Signed-off-by: Xiaolong Zhang <xiaolong.zhang@unisoc.com>
Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Link: https://lkml.kernel.org/r/20200304072730.9193-2-zhang.lyra@gmail.com


Signed-off-by: Stephen Boyd <sboyd@kernel.org>