power: qpnp-smbcharger: Add support to read max_voltage_design

Add support to read the max_voltage_design of a battery which is
needed for userspace. Since POWER_SUPPLY_VOLTAGE_MAX_DESIGN for
battery power supply is not directly supported, provide
the support for it by exporting this property from bms power supply.

CRs-Fixed: 695481
Change-Id: Ie81efabb8c9d8addf5da51c6f4be31f0a60420cd
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>