x86/PCI: Expand the x86_msi_ops to have a restore MSIs.

The MSI restore function will become a function pointer in an
x86_msi_ops struct. It defaults to the implementation in the
io_apic.c and msi.c. We piggyback on the indirection mechanism
introduced by "x86: Introduce x86_msi_ops".

Cc: x86@kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: linux-pci@vger.kernel.org
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

arch/x86/kernel/x86_init.c

@@ -114,4 +114,5 @@ struct x86_msi_ops x86_msi = {
 	.setup_msi_irqs = native_setup_msi_irqs,
 	.teardown_msi_irq = native_teardown_msi_irq,
 	.teardown_msi_irqs = default_teardown_msi_irqs,
+	.restore_msi_irqs = default_restore_msi_irqs,
 };