powerpc/pci: Use of_irq_parse_and_map_pci() helper

[Mathieu Malaterre]

Hi Rob,

I can no longer boot my old Mac Mini G4 using a custom config. After a
tedious bisect it appears that (*). Since Mac Mini does not provide
any serial port I cannot provide a kernel message dump (wish there was
some kind of null modem serial cable). All I can see is some crazy
stuff going on with ATA DMA/66 & DMA/100.

Is there anything suspicious in this commit which may prevent this
machine to boot ?

Thanks much,

(*)
$ git bisect good
59f47eff03a08cd2d91310f1c15a5343fa0071e5 is the first bad commit
commit 59f47eff03a08cd2d91310f1c15a5343fa0071e5
Author: Rob Herring <robh at kernel.org>
Date:   Thu Jan 4 15:12:14 2018 -0600

    powerpc/pci: Use of_irq_parse_and_map_pci() helper

    Instead of calling both of_irq_parse_pci() and irq_create_of_mapping(),
    call of_irq_parse_and_map_pci(), which does the same thing. This will allow
    making of_irq_parse_pci() a private, static function.

    This changes the logic slightly in that the fallback path will also be
    taken if irq_create_of_mapping() fails internally.

    Signed-off-by: Rob Herring <robh at kernel.org>
    [bhelgaas: fold in virq init from Stephen Rothwell <sfr at canb.auug.org.au>]
    Signed-off-by: Bjorn Helgaas <bhelgaas at google.com>
    Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
    Cc: Paul Mackerras <paulus at samba.org>
    Cc: Michael Ellerman <mpe at ellerman.id.au>

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