PCI: iproc: Remove unused struct iproc_pcie.irqs[]

Remove unused struct iproc_pcie member irqs[] and unused #define
IPROC_PCIE_MAX_NUM_IRQS.

Signed-off-by: Ray Jui <rjui@broadcom.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>