lantiq: Fix initialization of the PCI IRQs when PCIe is also enabled

There are already ifx_pcie_bios_{map_irq,plat_dev_init} hooks defined in
ifxmips_pcie.c. Instead of defining a new hook we simply re-use the
existing ones (this is basically what the lantiq BSP code does).

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>

SVN-Revision: 45718