power: qpnp-qg: Add QG voltage-only mode

In voltage only mode, QG hardware only samples
the VBAT and SOC is determined based on this. The
V only mode does not support QG the following QG
features - capacity learning, ESR estimation,
TCSS and BASS.

POWER_SUPPLY_FG_TYPE exposes the QG_V or QG_V_I based
QG configuration.

Change-Id: I6207f45f506ab595bd261a297abdd8f40990c8d3
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>