PM: devfreq: init performance/powersave governor

Performance and powersave governor's get_target_freq
is not called if driver chooses one of these two governors.
Add init function in governor profile to call update_devfreq
which will call get_target_freq subsequently.

Signed-off-by: Xiaoguang Chen <chenxg@marvell.com>
Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>