svm: Introduce AMD IOMMU avic_ga_log_notifier

This patch introduces avic_ga_log_notifier, which will be called
by IOMMU driver whenever it handles the Guest vAPIC (GA) log entry.

Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>