iommu/vt-d: Don't clobber posted vCPU IRTE when host IRQ affinity changes

iommu/vt-d: Don't clobber posted vCPU IRTE when host IRQ affinity changes

Don't overwrite an IRTE that is posting IRQs to a vCPU with a posted MSI
entry if the host IRQ affinity happens to change.  If/when the IRTE is
reverted back to "host mode", it will be reconfigured as a posted MSI or
remapped entry as appropriate.

Drop the "mode" field, which doesn't differentiate between posted MSIs and
posted vCPUs, in favor of a dedicated posted_vcpu flag.  Note!  The two
posted_{msi,vcpu} flags are intentionally not mutually exclusive; an IRTE
can transition between posted MSI and posted vCPU.

Fixes: ed1e48ea4370 ("iommu/vt-d: Enable posted mode for device MSIs")
Cc: stable@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20250315025135.2365846-3-seanjc@google.com
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>