PCI: aardvark: Use PCI_NUM_INTX

Switch from using a custom LEGACY_IRQ_NUM macro to the generic PCI_NUM_INTX
definition for the number of INTx interrupts.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>