ACPI: use kstrto*() instead of simple_strto*()

simple_strto*() are obsolete; use kstrto*() instead. Add proper error
checking.

Signed-off-by: Christoph Jaeger <christophjaeger@linux.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>