[U-Boot] rockchip: rk3399-puma: set gpio4cd iodomain to 1.8V

[Philipp Tomsich]

> The PCIe reset signal is connected to GPIO4_C6 on the Puma
> module. This pin is supplied by 1.8V, but the default iodomain
> setting is 3.0V and in this situation the pin is unable to go
> high.
> 
> Linux assumes that this signal works in early boot
> as PCIe is probed before loading the iodomain driver.
> 
> Make PCIe work in Linux by setting the gpio4cd iodomain to 1.8V.
> 
> Signed-off-by: Jakob Unterwurzacher <jakob.unterwurzacher at theobroma-systems.com>
> Acked-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>
> ---
> 
>  board/theobroma-systems/puma_rk3399/puma-rk3399.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 

Reviewed-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>