Input: add Spreadtrum vibrator driver

This patch adds the Spreadtrum vibrator driver, which embedded in the
Spreadtrum SC27xx series PMICs.

Signed-off-by: Xiaotong Lu <xiaotong.lu@spreadtrum.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>