Add support for Extended Destination ID

Description:

KVM added support for (re)using some of the reserved fields in the RTE in order to address APIC IDs > 255 without requiring an IOMMU with interrupt remapping support: http://david.woodhou.se/15-bit-msi.pdf (See Option 1).
Add support for doing the same in Xen, will require changes to the hypervisor and QEMU.
There's a CPUID bit reserved in Xen to announce support for the feature: https://xenbits.xen.org/gitweb/?p=xen.git;h=f5592322062f7912dc45b30606f20691f6e1c3ee
Setting the CPUID bit requires coordination in order for both the hypervisor and QEMU to properly handle it.

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