VT-d: posted interrupts require interrupt remapping

VT-d: posted interrupts require interrupt remapping

Initially I had just noticed the unnecessary indirection in the call
from pi_update_irte(). The generic wrapper having an iommu_intremap
conditional made me look at the setup code though. So first of all
enforce the necessary dependency.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 6c54663786d9f1ed04153867687c158675e7277d
master date: 2019-04-09 15:12:07 +0200