kernel: rtl836x: convert to gpiod API

kernel: rtl836x: convert to gpiod API

This is the recommended way for the OF based platform.

Tested-on TP-Link TL-WR2543N with RTL8367 switch:
```
root@OpenWrt:~# dmesg |grep -i rtl
[    7.941126] rtl8367 rtl8367: cannot find mdio node phandle
[    7.947562] rtl8367 rtl8367: RTL8367R ver. 0 chip found
[    9.056830] rtl8367 rtl8367: cpu_port:9, assigned to extif0
root@OpenWrt:~# cat /sys/kernel/debug/gpio
gpiochip0: GPIOs 512-529, parent: platform/18040000.gpio, 18040000.gpio:
 gpio-512 (                    |lime:status         ) out lo ACTIVE LOW
 gpio-513 (                    |rtl836x-sda         ) in  hi
 gpio-518 (                    |rtl836x-sck         ) in  lo
 gpio-520 (                    |lime:usb            ) out hi ACTIVE LOW
 gpio-523 (                    |reset               ) in  hi IRQ ACTIVE LOW
 gpio-524 (                    |wps                 ) in  hi IRQ ACTIVE LOW
```

Signed-off-by: Shiji Yang <yangshiji66@outlook.com>
Link: https://github.com/openwrt/openwrt/pull/21143
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>