x86: cleanup some remaining usages of NR_CPUS where s/b nr_cpu_ids

Impact: Reduce future system panics due to cpumask operations using NR_CPUS

Insure that code does not look at bits >= nr_cpu_ids as when cpumasks are
allocated based on nr_cpu_ids, these extra bits will not be defined.

Also some other minor updates:

   * change in to use cpu accessor function set_cpu_present() instead of
     directly accessing cpu_present_map w/cpu_clear() [arch/x86/kernel/reboot.c]

   * use cpumask_of() instead of &cpumask_of_cpu() [arch/x86/kernel/reboot.c]

   * optimize some cpu_mask_to_apicid_and functions.

Signed-off-by: Mike Travis <travis@sgi.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/msr.c

@@ -136,7 +136,7 @@ static int msr_open(struct inode *inode, struct file *file)
 	lock_kernel();
 	cpu = iminor(file->f_path.dentry->d_inode);
 
-	if (cpu >= NR_CPUS || !cpu_online(cpu)) {
+	if (cpu >= nr_cpu_ids || !cpu_online(cpu)) {
 		ret = -ENXIO;	/* No such CPU */
 		goto out;
 	}