AT91: MACB support

The Atmel MACB Ethernet peripheral is also integrated in the AT91SAM9260
and AT91SAM9263 processors.  The differences from the AVR32 version are:
      * Single peripheral clock.
      * MII/RMII selection bit is inverted.
      * Clock enable bit.

Original patch from Patrice Vilchez.

Signed-off-by: Andrew Victor <andrew@sanpeople.com>
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>