cpumask: limit visibility of FORCE_NR_CPUS

In current form, FORCE_NR_CPUS is visible to all users building their
kernels, even not experts.  It is also set in allmodconfig or
allyesconfig, which is not a correct behavior.

This patch fixes it.  It also changes the parameter short description:
removes implementation details and highlights the effect of the change.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Yury Norov <[email protected]>
Suggested-by: Geert Uytterhoeven <[email protected]>
Suggested-by: Linus Torvalds <[email protected]>
Reviewed-by: Valentin Schneider <[email protected]>
Cc: Alexey Klimov <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Eric Biggers <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rasmus Villemoes <[email protected]>
Cc: Sander Vanheule <[email protected]>
Cc: Stephen Rothwell <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

lib/Kconfig

@@ -529,8 +529,8 @@ config CPUMASK_OFFSTACK
 	  stack overflow.
 
 config FORCE_NR_CPUS
-       bool "NR_CPUS is set to an actual number of CPUs"
-       depends on SMP
+       bool "Set number of CPUs at compile time"
+       depends on SMP && EXPERT && !COMPILE_TEST
        help
          Say Yes if you have NR_CPUS set to an actual number of possible
          CPUs in your system, not to a default value. This forces the core