perf/x86/uncore/hsw-ep: Handle systems with only two SBOXes

There was another report of a boot failure with a #GP fault in the
uncore SBOX initialization. The earlier work around was not enough
for this system.

The boot was failing while trying to initialize the third SBOX.

This patch detects parts with only two SBOXes and limits the number
of SBOX units to two there.

Stable material, as it affects boot problems on 3.18.

Tested-by: Andreas Oehler <andreas@oehler-net.de>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <stable@vger.kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Yan, Zheng <zheng.z.yan@intel.com>
Link: http://lkml.kernel.org/r/1420583675-9163-1-git-send-email-andi@firstfloor.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>