ARM: dts: msm: make refgen regulator not always-on for SDM670

Remove always-on property from refgen regulator device node
and consider runtime enable/disable votes from CSI and DSI
clients.

Change-Id: Ib8c5ac06d06e2a0848613a61dc19249492638660
Signed-off-by: Tirupathi Reddy <tirupath@codeaurora.org>