regulator: max8998: Add charger regulator

The max8998 has a current regulator for charging control.  The
charger driver in drivers/power/supply/max8998_charger.c has a
comment in it stating that 'charger control is done by a current
regulator "CHARGER"', but this regulator was never added until
now.

The current values have been extracted from a downstream driver
for the SGH-T959V.

Signed-off-by: Jonathan Bakker <xc-racer2@live.ca>
Link: https://lore.kernel.org/r/BN6PR04MB0660E1F4A3D5A348BE88311CA3BA0@BN6PR04MB0660.namprd04.prod.outlook.com


Signed-off-by: Mark Brown <broonie@kernel.org>