x86/kconfig: Bump default NR_CPUS from 8 to 64 for 64-bit configuration

Default NR_CPUS==8 is not enough to cover high-end desktop
configuration: Haswell-E has upto 16 threads.

Let's increase default NR_CPUS to 64 on 64-bit configuration.
With this value CPU bitmask will still fit into one unsigned long.

Default for 32-bit configuration is still 8: it's unlikely
anybody will run 32-bit kernels on modern hardware.

As an alternative we could bump NR_CPUS to 128 to cover all
dual-processor servers with some margin.

For reference: Debian and Suse build their kernels with
NR_CPUS==512, Fedora -- 1024.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1431080745-19792-1-git-send-email-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/Kconfig

@@ -851,7 +851,8 @@ config NR_CPUS
 	default "1" if !SMP
 	default "8192" if MAXSMP
 	default "32" if SMP && X86_BIGSMP
-	default "8" if SMP
+	default "8" if SMP && X86_32
+	default "64" if SMP
 	---help---
 	  This allows you to specify the maximum number of CPUs which this
 	  kernel will support.  If CPUMASK_OFFSTACK is enabled, the maximum