power: qpnp-bms: add qpnp bms driver

QPNP BMS registers a power supply of type POWER_SUPPLY_TYPE_BMS,
which provides additional properties to the battery power supply
registered by the QPNP charger.

Currently the BMS reports hard coded constants. It reports SOC as 50%,
instantaneous current as 0 uA, and full charge as 0 uAh.

Change-Id: I9a6c80846abeb0f1fe9534afb2b768256ab4795e
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>