msm: qpnp-vibrator: Add sysfs interface for intensity

To control the Haptic intensity using sysfs interface.

2014-07-08	Scott Mertz	msm: vibrator: Add min/max voltage sysfs entries
2016-04-05	Danny Baumann	msm: vibrator: Properly unregister device files
2016-04-05	Danny Baumann	msm: vibrator: Add a sysfs node for the default (boot-up) level.

Change-Id: I53f484753793e56789feaefd638688b74e4c9324
Signed-off-by: SpaceKiller <alexisalbo.1@gmail.com>