x86, irq: update_mptable needs pci_routeirq

To get all device irq routing and to save them.

This is basically an implicit pci=routeirq enablement if (and on if)
the update_mptable boot option (which is off by default) has been
specified.

[ Impact: extend the update_mptable boot opion's scope ]

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
LKML-Reference: <4A0DB7B4.4060702@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>