nohz: ensure users are aware boot CPU is not NO_HZ_FULL

This bit of information is in the Kconfig help text:

  "Note the boot CPU will still be kept outside the range to
  handle the timekeeping duty."

However neither the variable NO_HZ_FULL_ALL, or the prompt
convey this important detail, so lets add it to the prompt
to make it more explicitly obvious to the average user.
Acked-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NPaul Gortmaker <paul.gortmaker@windriver.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1391711781-7466-1-git-send-email-paul.gortmaker@windriver.comSigned-off-by: NFrederic Weisbecker <fweisbec@gmail.com>

kernel/time/Kconfig

@@ -124,7 +124,7 @@ config NO_HZ_FULL
 endchoice
 
 config NO_HZ_FULL_ALL
-       bool "Full dynticks system on all CPUs by default"
+       bool "Full dynticks system on all CPUs by default (except CPU 0)"
        depends on NO_HZ_FULL
        help
          If the user doesn't pass the nohz_full boot option to