exec: introduce address_space_get_iotlb_entry()

exec: introduce address_space_get_iotlb_entry()

This patch introduces a helper to query the iotlb entry for a
possible iova. This will be used by later device IOTLB API to enable
the capability for a dataplane (e.g vhost) to query the IOTLB.

Cc: Paolo Bonzini <[email protected]>
Cc: Peter Crosthwaite <[email protected]>
Cc: Richard Henderson <[email protected]>
Acked-by: Paolo Bonzini <[email protected]>
Signed-off-by: Jason Wang <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>