ACPI, x86: expose some IO-APIC routines when CONFIG_ACPI=n

Some IO-APIC routines are ACPI specific now, but need to
be exposed when CONFIG_ACPI=n for the benefit of SFI.

Remove #ifdef ACPI around these routines:

io_apic_get_unique_id(int ioapic, int apic_id);
io_apic_get_version(int ioapic);
io_apic_get_redir_entries(int ioapic);

Move these routines from ACPI-specific boot.c to io_apic.c:

uniq_ioapic_id(u8 id)
mp_find_ioapic()
mp_find_ioapic_pin()
mp_register_ioapic()

Also, since uniq_ioapic_id() is now no longer static,
re-name it to io_apic_unique_id() for consistency
with the other public io_apic routines.

For simplicity, do not #ifdef the resulting code ACPI || SFI,
thought that could be done in the future if it is important
to optimize the !ACPI !SFI IO-APIC x86 kernel for size.

Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Cc: x86@kernel.org