power: smb5: add support to export "POWER_SUPPLY_PROP_CHARGE_FULL"

Add support to expose "POWER_SUPPLY_PROP_CHARGE_FULL" from battery
power supply class.
While at it, create a common function to read properties from "bms"
power_supply_class.

Change-Id: I5980006c4429a835c0f5bf674f5de2657d990517
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>