power: qpnp-fg: Add support to control the SW based Rbias

Commit 511c34bf
(power: qpnp-fg: Configure SW based Rbias and manage it) added
the support to configure SW based Rbias. However it enables that
feature by default which is not required for some boards. Add a
boolean property to select the feature on need basis.

CRs-Fixed: 743954
Change-Id: Id96d7c06ef4654a088f0ec256d25f98ff6165fb6
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>