power: qpnp-smbcharger: Add support for voltage_max property

Provide support to read or configure the float voltage of
the charger through POWER_SUPPLY_PROP_VOLTAGE_MAX property.

CRs-Fixed: 695481
Change-Id: Ib8b22fd937e504385a90bb1143e5364d08868460
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>