drivers/pcie: Add a marco for fixed or MSI IRQ

This is meant to be called by drivers on PCIe BUS with a fixed (from
DTS) IRQ or an MSI one. I.e.: all drivers without a runtime IRQ
detection/allocation.

The arch-specific macro is required to be implemented relevantly.

Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>