power: supply: axp20x_usb_power: add support for AXP813

This adds support for AXP813 PMIC. It is almost the same as AXP22X but
has a different current limit.

Signed-off-by: Quentin Schulz <quentin.schulz@bootlin.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>