[CPUFREQ] implement !CONFIG_CPU_FREQ stub for cpufreq_unregister_notifier()

Callsites such as arch/powerpc/oprofile/op_model_cell.c are having to
open-code #ifdef CONFIG_CPU_FREQ only to be able to get at the full definition
of cpufreq_unregister_notifier(), because no empty stub is available for the
!CONFIG_CPU_FREQ case.  Let's provide one, to be able to remove such #ifdef's
from the rest of the kernel tree -- those will come in a subsequent patch.

Signed-off-by: Satyam Sharma <satyam@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Jones <davej@redhat.com>

include/linux/cpufreq.h

@@ -32,12 +32,24 @@
  *                     CPUFREQ NOTIFIER INTERFACE                    *
  *********************************************************************/
 
-int cpufreq_register_notifier(struct notifier_block *nb, unsigned int list);
-int cpufreq_unregister_notifier(struct notifier_block *nb, unsigned int list);
-
 #define CPUFREQ_TRANSITION_NOTIFIER	(0)
 #define CPUFREQ_POLICY_NOTIFIER		(1)
 
+#ifdef CONFIG_CPU_FREQ
+int cpufreq_register_notifier(struct notifier_block *nb, unsigned int list);
+int cpufreq_unregister_notifier(struct notifier_block *nb, unsigned int list);
+#else		/* CONFIG_CPU_FREQ */
+static inline int cpufreq_register_notifier(struct notifier_block *nb,
+						unsigned int list)
+{
+	return 0;
+}
+static inline int cpufreq_unregister_notifier(struct notifier_block *nb,
+						unsigned int list)
+{
+	return 0;
+}
+#endif		/* CONFIG_CPU_FREQ */
 
 /* if (cpufreq_driver->target) exists, the ->governor decides what frequency
  * within the limits is used. If (cpufreq_driver->setpolicy> exists, these