macb: unify at91 and avr32 platform data

Both at91 and avr32 defines its own platform data structure for
the macb driver and both share common structures though at91
includes a currently unused phy_irq_pin.  Create a common
macb_platform_data for macb that both at91 and avr32 can use.  In
future we can use this to support other architectures that use the
same IP block with the macb driver.

v2: rename eth_platform_data to macb_platform_data and allow at91_ether
to share the platform data with macb.

Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Tested-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>