intel_iommu: introduce vtd_reset_caches()

intel_iommu: introduce vtd_reset_caches()

Provide the function and use it in vtd_init().  Used to reset both
context entry cache and iotlb cache for the whole IOMMU unit.

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit 06aba4ca52fd2c8718b8ba486f22f0aa7c99ed55)
*functional dep. for 2cc9ddcceb
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>