regulator: Add QTI LCDB regulator driver

Add snapshot of QTI LCDB regulator driver that helps with
controlling display bias voltage rails for LCD panels.
This snapshot is taken as of msm-4.19
commit 4dfd3f4203aa3ae ("mhi: core: ensure non-zero session or sequence
ID values").

Change-Id: Idf30c348194870e94a65af4a6cc4d830f60e4e7c
Signed-off-by: Jishnu Prakash <jprakash@codeaurora.org>