x86: SB600: skip IRQ0 override if it is not routed to INT2 of IOAPIC

Impact: fix hung bootup and other misbehavior on certain laptops

On some more HP laptops BIOS reports an IRQ0 override
but the SB600 chipset is configured such that timer
interrupts go to INT0 of IOAPIC.

Check IRQ0 routing and if it is routed to INT0 of IOAPIC skip the
timer override.

See following bug reports:

  http://bugzilla.kernel.org/show_bug.cgi?id=11715
  http://bugzilla.kernel.org/show_bug.cgi?id=11516

Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Cc: <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>