power: supply: ab8500: Standardize CV voltage

The voltage used in the constant voltage phase of the charging
exist in struct power_supply_battery_info as
constant_charge_voltage_max_uv.

Switch the custom property normal_vol_lvl to this and
consequentially change everything that relates to this value
over to using microvolts rather than millivolts so
we align internal representation of current with the
power core. Prefix every variable we change with *_uv
to indicate the unit everywhere but also to make sure
we do not miss any outlier.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>