power_supply: Add QG_VBMS_MODE property

Add Qgauge Voltage only mode property which indicates whether
Qgauge running in Voltage-only mode of Qgauge or Normal Qgauge mode.

CRs-Fixed: 2374455
Change-Id: Ic14ab3085a264b127bb5fb533328375d52abaf40
Signed-off-by: Vamshi Krishna B V <vbv@codeaurora.org>