gitv3_its: fixes for multiple GIC ITS blocks

First pass of support for multiple GIC ITS blocks with ACPI.
Changes are to:

• register the correct subset of interrupts with pic_register in case of ACPI.
• initialize just the cpu interface for the first ITS, when domain information is not avialable. This has to be done until we split the per-CPU init to do LPI setup just once.
• remove duplicate check for the GIC ITS domain, the sc_cpus are setup from domain, so the check again in per-CPU init seems unnecessary.

Reviewed by: andrew
Differential Revision: https://reviews.freebsd.org/D17841