PCI MSI: Unify msi_free_irqs() and msix_free_all_irqs()

Unify msi_free_irqs() and msix_free_all_irqs(), and rename it to a
common void function free_msi_irqs().

And relocate the common function to where the prototype is located now.

Reviewed-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>