Add support for GPIOs for SMSC LAN95xx chips.
There might be 11 GPIOs in total.
Last three GPIOs  (offsets 8-11, 0-based) are shared with FDX, LNKA, SPD
LEDs respectively. The LEDs are driven by chip by default at startup time.
Once the corresponding GPIO is requested, the chip LED drive logic is disabled.

Based on commented out code presumably from SMSC original driver.
https://github.com/olerem/barebox/blob/master/drivers/net/usb/smsc95xx.c