intel_idle: Use more common logging style

Remove #define PREFIX and add #define pr_fmt to use more common logging.

Miscellanea:

o Add missing newline to format
o Convert a single printk without KERN_<LEVEL> to pr_info

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>