intel_idle: use pr_info() instead of printk()

Substitute 'printk()' with 'pr_info()', because 'intel_idle' already uses
'pr_debug()', so using 'pr_info()' will be more consistent.

In addition to this, this patch addresses  the following checkpatch.pl
warning:
  WARNING: printk() should include KERN_<LEVEL> facility level

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Reviewed-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>