power: axp288_charger: axp288 charger driver

This patch adds new power supply charger driver support
for X-Power AXP288 PMIC integrated charger.

This driver interfaces with the axp20x mfd driver as a cell
and listens to extcon cable events for setting up charging.

Signed-off-by: Ramakrishna Pallala <ramakrishna.pallala@intel.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Sebastian Reichel <sre@kernel.org>