Drop the __init from pcibios_map_irq() to make this section mis-
match go away:
WARNING: vmlinux.o(.text+0x56acd4): Section mismatch in reference from the function pcibios_scanbus() to the function .init.text:pcibios_map_irq()
The function pcibios_scanbus() references
the function __init pcibios_map_irq().
This is often because pcibios_scanbus lacks a __init
annotation or the annotation of pcibios_map_irq is wrong.