rockchip: rk3188: fix early uart setup

rockchip: rk3188: fix early uart setup

Commit 7a6d7d3e1279 ("rockchip: pinctrl: rk3188: Move the iomux definitions
into pinctrl-driver") moved the iomux settings out of the grf header
to prevent conflicts with the iomux definitions of other rockchip socs.

This also breaks the early uart setup, as the iomux for uart2 are needed.
To fix that just put the tiny amount of needed iomux definitions next to
the early uart code.

Fixes: 7a6d7d3e1279 ("rockchip: pinctrl: rk3188: Move the iomux definitions into pinctrl-driver")
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>