ARM: at91/dt: fix macb compatible strings

Some at91 SoCs embed a 10/100 Mbit Ethernet IP, that is based on the
at91sam9260 SoC.
Fix at91 DTs accordingly.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Reviewed-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>