Only allow the pic type to be either a PIC or MSI type. All interrupt
controller drivers handle either MSI/MSI-X interrupts, or regular
interrupts, as such enforce this in the interrupt handling framework.
If a later driver was to handle both it would need to create one of each.

This will allow future changes to allow the xref space to overlap, but
refer to different drivers.

Obtained from: ABT Systems Ltd
Sponsored by: The FreeBSD Foundation
X-Differential Revision: https://reviews.freebsd.org/D8616