intr-remap: allow disabling source id checking

Allow disabling the source id checking while programming the interrupt
remap table entry. Useful for debugging or working around the broken
source id checks on some platforms.

Signed-off-by: Chris Wright <chrisw@redhat.com>
Acked-by: Suresh Siddha <suresh.b.siddha@intel.com>
Acked-by: Weidong Han <weidong.han@intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>