vfio/fsl-mc: Add irq infrastructure for fsl-mc devices

This patch adds the skeleton for interrupt support
for fsl-mc devices. The interrupts are not yet functional,
the functionality will be added by subsequent patches.

Signed-off-by: Bharat Bhushan <Bharat.Bhushan@nxp.com>
Signed-off-by: Diana Craciun <diana.craciun@oss.nxp.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>