mfd: axp20x: Add supported cells for AXP803

Parts of the AXP803 are compatible with their counterparts on the AXP813.
These include the GPIO, ADC, AC and battery power supplies.

Signed-off-by: Oskari Lemmela <oskari@lemmela.net>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Tested-by: Vasily Khoruzhick <anarsoul@gmail.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>