pinctrl: rockchip: Split the common set_drive() func into per Soc

pinctrl: rockchip: Split the common set_drive() func into per Soc

As the common set_mux func(), implement the feature at the own file
for each Soc.

Signed-off-by: David Wu <david.wu@rock-chips.com>
Signed-off-by: Kever Yang <kever.yang@rock-chips.com>