VT-d: always clean up dpci timers.

VT-d: always clean up dpci timers.
Message-ID: <20110718163848.GD18276@whitby.uk.xensource.com>
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If a VM has all its PCI devices deassigned, need_iommu(d) becomes
false but it might still have DPCI EOI timers that were init_timer()d
but not yet kill_timer()d.  That causes xen to crash later because the
linked list of inactive timers gets corrupted, e.g.:

(XEN) Xen call trace:
(XEN)    [<ffff82c480126256>] set_timer+0x1c2/0x24f
(XEN)    [<ffff82c48011fbf8>] schedule+0x129/0x5dd
(XEN)    [<ffff82c480122c1e>] __do_softirq+0x7e/0x89
(XEN)    [<ffff82c480122c9d>] do_softirq+0x26/0x28
(XEN)    [<ffff82c480153c85>] idle_loop+0x5a/0x5c
(XEN)
(XEN)
(XEN) ****************************************
(XEN) Panic on CPU 0:
(XEN) Assertion 'entry->next->prev == entry' failed at
/local/scratch/tdeegan/xen-unstable.hg/xen/include:172
(XEN) ****************************************

The following patch makes sure that the domain destruction path always
clears up the DPCI state even if !needs_iommu(d).

Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com>