realtek: rtl838x: Switch GS1900 rtl8231 driver

Update the devicetree files to switch the GS1900 devices over to the new
pinctrl and GPIO driver. Enable the drivers to ensure the nodes can be
used.

This may fix issues caused by bad RMW behaviour on the GPIO data lines,
or glitches due to setting the pin direction before the pin level.

Although the driver supports retaining GPIO state after a warm boot,
some bootloaders appear to apply a default configuration on boot, which
may cause an interrupt in PoE-PSE support.

Signed-off-by: Sander Vanheule <sander@svanheule.net>
(cherry picked from commit 5141e2d8)