regulator: qpnp-labibb: Add support for TTW on PMI8950

Add TTW configuration for PMI8950. Also, add a DT property
(qcom,labibb-ttw-force-lab-on) to keep LAB always-on in TTW mode.
Presently, this property is only required for PMI8950.

CRs-Fixed: 958285 962662
Change-Id: Iec79a6f752067d96fc62a8e9d629c39f4db5ab9f
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>