For RTL839x, the driver was producing frequent timeouts on bus accesses.
Increasing the timeout to the one from a recent Realtek SDK resolves
these timeouts. To minimize overhead on different SoCs, each controller
can specify their own timeout.

This also add support for the register format as used on RTL93xx.
Support is added for the RTL930x "ext gpio" controller.

Signed-off-by: Sander Vanheule <sander@svanheule.net>