pinctrl: rockchip: Fix the rk3399 gpio0 and gpio1 banks' drv_offset at pmu grf

The offset of gpio0 and gpio1 bank drive strength is 0x8, not 0x4.
But the mux is 0x4, we couldn't use the IOMUX_WIDTH_4BIT flag, so
we give them actual offset.

Signed-off-by: David Wu <david.wu@rock-chips.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>