Driver for the Atmel MACB on-chip ethernet module.

Tested on AVR32/AT32AP7000/ATSTK1000. I've heard rumours that it works
with AT91SAM9260 as well, and it may be possible to share some code with
the at91_ether driver for AT91RM9200.

Hardware documentation can be found in the AT32AP7000 data sheet,
which can be downloaded from

http://www.atmel.com/dyn/products/datasheets.asp?family_id=682

Changes since previous version:
  * Probe for PHY ID instead of depending on it being provided through
    platform_data.
  * Grab initial ethernet address from the MACB registers instead
    of depending on platform_data.
  * Set MII/RMII mode correctly.

These changes are mostly about making the driver more compatible with
the at91 infrastructure.
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>