powerpc/pci: Use of_irq_parse_and_map_pci() helper

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 <[email protected]>
[bhelgaas: fold in virq init from Stephen Rothwell <[email protected]>]
Signed-off-by: Bjorn Helgaas <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Michael Ellerman <[email protected]>