KVM: SVM: Take and hold ir_list_lock across IRTE updates in IOMMU

KVM: SVM: Take and hold ir_list_lock across IRTE updates in IOMMU

Now that svm_ir_list_add() isn't overloaded with all manner of weird
things, fold it into avic_pi_update_irte(), and more importantly take
ir_list_lock across the irq_set_vcpu_affinity() calls to ensure the info
that's shoved into the IRTE is fresh.  While preemption (and IRQs) is
disabled on the task performing the IRTE update, thanks to irqfds.lock,
that task doesn't hold the vCPU's mutex, i.e. preemption being disabled
is irrelevant.

Link: https://lore.kernel.org/r/20250611224604.313496-40-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>