Correct MPIC order of attachment
If MPIC happens to be a slave interrupt controller (as on Armada38x),
it should be attached after primary interrupt controller.
Thus BUS_PASS_ORDER_LATE was added to default BUS_PASS_INTERRUPT.
This change doesn't affect the cases when MPIC is standalone IC.
Submitted by: Bartosz Szczepanek <firstname.lastname@example.org>
Obtained from: Semihalf
Sponsored by: Stormshield, Netgate
Reviewed by: loos
Differential revision: https://reviews.freebsd.org/D10715