dev: net/i8254xGBe add two more wakeup registers to ignore

dev: net/i8254xGBe add two more wakeup registers to ignore

There are drivers writing to WUFC uncondtionally of anything.  In order to
not panic gem5 in these cases, ignore writes to WUFC and WUS as we do for
WUC.  Similarly return 0 (default reset value) on reads.

Testing Done: Booted in FS with such a driver revision which would
previously panic and now boots fine.

Reviewed at http://reviews.gem5.org/r/3791/

Signed-off-by: Jason Lowe-Power <jason@lowepower.com>