x86, intr-remap: Avoid irq_chip mask/unmask in fixup_irqs() for intr-remapping

In the presence of interrupt-remapping, irqs will be migrated in
the process context and we don't do (and there is no need to)
irq_chip mask/unmask while migrating the interrupt.

Similarly fix the fixup_irqs() that get called during cpu
offline and avoid calling irq_chip mask/unmask for irqs that are
ok to be migrated in the process context.

While we didn't observe any race condition with the existing
code, this change takes complete advantage of
interrupt-remapping in the newer generation platforms and avoids
any potential HW lockup's (that often worry Eric :)

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Acked-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: garyhade@us.ibm.com
LKML-Reference: <20091026230001.661423939@sbs-t61.sc.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>