Input: pm8xxx-vibrator - migrate to regmap APIs

Use the regmap APIs for this driver instead of custom pm8xxx
APIs. This breaks this driver's dependency on the pm8xxx APIs and
allows us to easily port it to other bus protocols in the future.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>