cpuidle-haltpoll: vcpu hotplug support

When cpus != maxcpus cpuidle-haltpoll will fail to register all vcpus
past the online ones and thus fail to register the idle driver.
This is because cpuidle_add_sysfs() will return with -ENODEV as a
consequence from get_cpu_device() return no device for a non-existing
CPU.

Instead switch to cpuidle_register_driver() and manually register each
of the present cpus through cpuhp_setup_state() callbacks and future
ones that get onlined or offlined. This mimmics similar logic that
intel_idle does.

Fixes: fa86ee90eb11 ("add cpuidle-haltpoll driver")
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/include/linux/cpuidle_haltpoll.h b/include/linux/cpuidle_haltpoll.h
index fe5954c..d50c1e0 100644
--- a/include/linux/cpuidle_haltpoll.h
+++ b/include/linux/cpuidle_haltpoll.h
@@ -5,11 +5,11 @@
 #ifdef CONFIG_ARCH_CPUIDLE_HALTPOLL
 #include <asm/cpuidle_haltpoll.h>
 #else
-static inline void arch_haltpoll_enable(void)
+static inline void arch_haltpoll_enable(unsigned int cpu)
 {
 }
 
-static inline void arch_haltpoll_disable(void)
+static inline void arch_haltpoll_disable(unsigned int cpu)
 {
 }
 #endif