iommu/amd: Fix interrupt remapping when disable guest_mode
Pass-through devices to VM guest can get updated IRQ affinity
information via irq_set_affinity() when not running in guest mode.
Currently, AMD IOMMU driver in GA mode ignores the updated information
if the pass-through device is setup to use vAPIC regardless of guest_mode.
This could cause invalid interrupt remapping.
Also, the guest_mode bit should be set and cleared only when
SVM updates posted-interrupt interrupt remapping information.