io_apic: Support APIC Extended Destination IDs

If APIC Extended Destination ID support is enabled, use it in APIC RTEs
by allowing APIC IDs up to 2^15 - 1 and encoding the high bits into
Intel "reserved" bits per the standard.

Reviewed by: kib
MFC after: 3 weeks
Sponsored by: Amazon
Differential Revision: https://reviews.freebsd.org/D55889