arch/x86/oprofile/op_model_amd.c: Perform initialisation on a single CPU

Disable preemption in init_ibs(). The function only checks the
ibs capabilities and sets up pci devices (if necessary). It runs
only on one cpu but operates with the local APIC and some MSRs,
thus it is better to disable preemption.

[    7.034377] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/483
[    7.034385] caller is setup_APIC_eilvt+0x155/0x180
[    7.034389] Pid: 483, comm: modprobe Not tainted 2.6.37-rc1-20101110+ #1
[    7.034392] Call Trace:
[    7.034400]  [<ffffffff812a2b72>] debug_smp_processor_id+0xd2/0xf0
[    7.034404]  [<ffffffff8101e985>] setup_APIC_eilvt+0x155/0x180
[ ... ]

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=22812

Reported-by:  <atswartz@gmail.com>
Signed-off-by: Robert Richter <robert.richter@amd.com>
Cc: oprofile-list@lists.sourceforge.net <oprofile-list@lists.sourceforge.net>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Dan Carpenter <error27@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@kernel.org>         [2.6.37.x]
LKML-Reference: <20110103111514.GM4739@erda.amd.com>
[ small cleanups ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>