ACPI: processor_throttling: Cleanup the printing messages

The log messages in processor_throttling.c is not in consistency,
we have some printk() calls with PREFIX, but some are not; also we
use pr_*() functions without prefix. So add pr_fmt() and unify
them with pr_*() functions.

While at it, fix some obvious coding style issues when going
through the functions.

Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>