clk: rockchip: rk3366: leave npll for VOP only

clk: rockchip: rk3366: leave npll for VOP only

We will need a pll to support all kinds of clock rate requirement
for HDMI which may change the rate at run time.

In order not to affect other clocks, remove the npll from the
parent list of other clocks and only DCLK_VOP(FULL or LITE) can
select npll as parent. Also add the ability for DCLK_VOP to set
the rate of its parent (which is now forced to NPLL).

Change-Id: I1e13ef1c4f1b9728f9c173454d5056780c47a95e
Signed-off-by: Feng Xiao <xf@rock-chips.com>