x86, msi: Introduce x86_msi.compose_msi_msg call-back

This call-back points to the right function for initializing
the msi_msg structure. The old code for msi_msg generation
was split up into the irq-remapped and the default case.

The irq-remapped case just calls into the specific Intel or
AMD implementation when the device is behind an IOMMU.
Otherwise the default function is called.

Signed-off-by: Joerg Roedel <joro@8bytes.org>
Acked-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
index 06db44f..ee4a17c 100644
--- a/arch/x86/kernel/x86_init.c
+++ b/arch/x86/kernel/x86_init.c
@@ -113,6 +113,7 @@
 EXPORT_SYMBOL_GPL(x86_platform);
 struct x86_msi_ops x86_msi = {
 	.setup_msi_irqs		= native_setup_msi_irqs,
+	.compose_msi_msg	= native_compose_msi_msg,
 	.teardown_msi_irq	= native_teardown_msi_irq,
 	.teardown_msi_irqs	= default_teardown_msi_irqs,
 	.restore_msi_irqs	= default_restore_msi_irqs,