pm8xxx-vibrator: exposed sysfs to modify voltage level
should show up as /sys/devices/platform/msm_ssbi.0/pm8921-core/pm8xxx-vib/amp

there are only 20 discrete steps though (12 to 31)

Change-Id: I4f0d3168a16d7a70f2fbbf21305879aa1ca5e7ec
Merge "pm8xxx-vibrator: exposed sysfs to modify voltage level should show up as /sys/devices/platform/msm_ssbi.0/pm8921-core/pm8xxx-vib/amp" into kk4.4