SMSC LAN91c111 Ethernet mac

Required properties:
- compatible = "smsc,lan91c111";
- reg : physical address and size of registers
- interrupts : interrupt connection

Optional properties:
- phy-device : see ethernet.txt file in the same directory
- reg-io-width : Mask of sizes (in bytes) of the IO accesses that
  are supported on the device.  Valid value for SMSC LAN91c111 are
  1, 2 or 4.  If it's omitted or invalid, the size would be 2 meaning
  16-bit access only.
- power-gpios: GPIO to control the PWRDWN pin
- reset-gpios: GPIO to control the RESET pin
