x86_iommu: move vtd_generate_msi_message in common file

x86_iommu: move vtd_generate_msi_message in common file

The vtd_generate_msi_message() in intel-iommu is used to construct a MSI
Message from IRQ. A similar function will be needed when we add interrupt
remapping support in amd-iommu. Moving the function in common file to
avoid the code duplication. Rename it to x86_iommu_irq_to_msi_message().
There is no logic changes in the code flow.

Signed-off-by: Brijesh Singh <[email protected]>
Suggested-by: Peter Xu <[email protected]>
Reviewed-by: Eduardo Habkost <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: "Michael S. Tsirkin" <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Richard Henderson <[email protected]>
Cc: Eduardo Habkost <[email protected]>
Cc: Marcel Apfelbaum <[email protected]>
Cc: Tom Lendacky <[email protected]>
Cc: Suravee Suthikulpanit <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>