gianfar: Use interface name in interrupt name to distinguish the source.

Interface name (ex. eth0) is used as the prefix for the interrupt name,
with _rx, _tx, and _er appended to distinguish multiple interrupts on
the same interface.

Signed-off-by: Dai Haruki <dai.haruki@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>