[IA64] Cleanup ACPI checksum warnings

[IA64] Cleanup ACPI checksum warnings

On bootup, I get a couple of these:

(XEN) ACPI Warning (tbutils-0219): Incorrect checksum in table [APIC] - CE, should be 04 [20070126]
(XEN) ACPI Warning (tbutils-0219): Incorrect checksum in table [APIC] - CE, should be 04 [20070126]

I don't remember seeing them before, but they're pretty easy to fix.
The problem is we update the lsapics, causing the checksum to be wrong,
then we look for platform interrupt sources, which spits out a warning,
and finally we look for the MADT again to fix the checksum, which also
prints a warning.  If we grab a pointer to the MADT before these, we can
update the checksum after each step and avoid the warnings.

Signed-off-by: Alex Williamson <alex.williamson@hp.com>