Fix build failure of AT91SAM9260.

The AT91RM9200 ethernet driver (at91_ether.c) stores platform data in a
"struct at91_eth_data" structure, but the AT91SAM9260 (and AT91SAM9263)
ethernet driver (macb.c) [developed on the AVR32 architecture] expects a
"struct eth_platform_data".

Since the platform data of the two drivers is very similar, we continue
to use the "struct at91_eth_data" for all AT91 processors but add a
    #define eth_platform_data      at91_eth_data
in board.h to keep the MACB driver happy.

Original patch by Jan Altenberg.
Signed-off-by: Andrew Victor <andrew@sanpeople.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>