pinctrl: rockchip: Add pinctrl support for rk3308

An iomux register contains 8 pins, each of which is represented
by 2 bits, but the register offset is 0x8.

For example, GRF_GPIO0A_IOMUX offset is 0x0, but GRF_GPIO0B_IOMUX
offset is 0x8, the offset 0x4 is reserved.

So add a type IOMUX_8WIDTH_2BIT to calculate offset.

Signed-off-by: David Wu <david.wu@rock-chips.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/drivers/pinctrl/rockchip/Makefile b/drivers/pinctrl/rockchip/Makefile
index 83913f6..fcf19f8 100644
--- a/drivers/pinctrl/rockchip/Makefile
+++ b/drivers/pinctrl/rockchip/Makefile
@@ -9,6 +9,7 @@
 obj-$(CONFIG_ROCKCHIP_RK3188) += pinctrl-rk3188.o
 obj-$(CONFIG_ROCKCHIP_RK322X) += pinctrl-rk322x.o
 obj-$(CONFIG_ROCKCHIP_RK3288) += pinctrl-rk3288.o
+obj-$(CONFIG_ROCKCHIP_RK3308) += pinctrl-rk3308.o
 obj-$(CONFIG_ROCKCHIP_RK3328) += pinctrl-rk3328.o
 obj-$(CONFIG_ROCKCHIP_RK3368) += pinctrl-rk3368.o
 obj-$(CONFIG_ROCKCHIP_RK3399) += pinctrl-rk3399.o