power: qpnp-charger: Add a regulator device to control flash led WAs

Flash led relies on SMBB to supply the 5V drive voltage. Add a regulator
device in qpnp-charger driver to support flash related workarounds in
SMBB.

While at it, add a SMBB temperature threshold workaround in the
regulator device. On certain devices SMBB/SMBBP over temperature
happened at default settings before flash module start thermal derating.
Raise the SMBB over temperature threshold when regulator enabled, and
restore to default setting when regulator disabled.

CRs-Fixed: 697457
Change-Id: I73dec98ea96b38937f2813794dc0beb7d5516e3a
Signed-off-by: Chunmei Cai <ccai@codeaurora.org>