ACPI / thermal: convert printk(LEVEL...) to pr_<lvl>

Convert printks to pr_* format. Additionally re-use PREFIX constant instead of
hardcoded strings.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>