pm8xxx-vibrator: exposed sysfs to modify voltage level

sysfs path: sys/devices/platform/msm_ssbi.0/pm8058-core/pm8xxx-vib/amp

credit: ngvincent
vigor: update proximity sensor levels
Revert "Faster scaling through lower end clocks"

Part of commit found here:
https://github.com/Snuzzo/funky_kernel/commit/1b53f437ced0973ef3b8edbffe77620437f47232