qpnp-smb2: add support to configure charge inhibit

Currently charge inhibit feature is enabled by default and the
charge inhibit threshold is not configurable. Add a device tree
parameter "qcom,chg-inhibit-threshold-mv" through which the
charge inhibit threshold can be configured. If the property is
not specified, then charge inhibit feature is kept disabled.

Change-Id: I464d720abc138e8cd9ba8d7f1704cd91f4408bee
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>