cpuidle-haltpoll: set haltpoll as preferred governor

Right now, guest current governors have the following ratings:

 * ladder            -> 10
 * teo               -> 19
 * menu              -> 20
 * haltpoll          -> 21
 * ladder + nohz=off -> 25

haltpoll governor got introduced and it is now the default governor given
its highest rating -- with ladder+nohz being the exception -- regardless of
idle driver in the guest. An example of an undesirable case is x86 KVM
guests with MWAIT which have intel_idle registered first, and consequently
will have haltpoll be used as governor which would get limited to a poll
state and state 1 and the other states wouldn't get used.

To keep the previous defaults we decrease rating of governor to 9 (below
current lowest rating) and thus rely on @governor switch on
cpuidle_register_driver() to tie in haltpoll idle driver and governor
together.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpuidle/cpuidle-haltpoll.c

@@ -34,6 +34,7 @@ static int default_enter_idle(struct cpuidle_device *dev,
 
 static struct cpuidle_driver haltpoll_driver = {
 	.name = "haltpoll",
+	.governor = "haltpoll",
 	.owner = THIS_MODULE,
 	.states = {
 		{ /* entry 0 is for polling */ },

drivers/cpuidle/governors/haltpoll.c

@@ -133,7 +133,7 @@ static int haltpoll_enable_device(struct cpuidle_driver *drv,
 
 static struct cpuidle_governor haltpoll_governor = {
 	.name =			"haltpoll",
-	.rating =		21,
+	.rating =		9,
 	.enable =		haltpoll_enable_device,
 	.select =		haltpoll_select,
 	.reflect =		haltpoll_reflect,