spidernet: change interrupt masks

This patch changes spidernet interrupt masks.

 - unmask GDAINVAINT. There is an operation to do by spidernet
   interrupt handler.
 - mask some interrupts. There are no operations in the interrupt handler.

Signed-off-by: Kou Ishizaki <kou.ishizaki@toshiba.co.jp>
Acked-by: Jens Osterkamp <jens@de.ibm.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>