x86/topology: Set x86_max_cores to 1 for CONFIG_SMP=n

Josef reported that the uncore driver trips over with CONFIG_SMP=n because
x86_max_cores is 16 instead of 12.

The reason is, that for SMP=n the extended topology detection is a NOOP and
the cache leaf is used to determine the number of cores. That's wrong in two
aspects:

1) The cache leaf enumerates the maximum addressable number of cores in the
   package, which is obviously not correct

2) UP has no business with topology bits at all.

Make intel_num_cpu_cores() return 1 for CONFIG_SMP=n

Reported-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: kernel-team <Kernel-team@fb.com>
Cc: Kan Liang <kan.liang@intel.com>
Link: http://lkml.kernel.org/r/761b4a2a-0332-7954-f030-c6639f949612@fb.com