Stop (trying to) renumber io apics.

It does not serve any purpose now, the io apic id is not seen by
software, and some Intel documents claim that the register is
implemented for FUD reasons. More, renumbering seems to not work on
new Intel machines which actually have mismatched MADT and hw IDs.

On older machines where separate APIC bus existed, unique numbering of
all APICs was required for bus arbitration to work, but it is no
longer true (that machines were SMP from pre-Pentium IV era).

When matching PCIe IOAPIC device against MADT-enumerated IOAPICs,
compare io_apic_id from BAR against io_apic_id read from the
MADT-pointed register page.

Reviewed by: jhb
Tested by: flo (previous version), pho
MFC after: 2 weeks
Differential revision: https://reviews.freebsd.org/D23965