powernow-k6: support 350MHz CPU

There exists 350MHz K6-2E+ CPU, so add it to the usual frequency table.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>