net: txgbe: use irq_domain for interrupt controller

In the current interrupt controller, the MAC interrupt acts as the
parent interrupt in the GPIO IRQ chip. But when the number of Rx/Tx
ring changes, the PCI IRQ vector needs to be reallocated. Then this
interrupt controller would be corrupted. So use irq_domain structure
to avoid the above problem.

Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>