power: supply: axp20x_ac_power: Fix reporting online status

AXP803/AXP813 have a flag that enables/disables the AC power supply
input. This flag does not affect the status bits in PWR_INPUT_STATUS.
Its effect can be verified by checking the battery charge/discharge
state (bit 2 of PWR_INPUT_STATUS), or by examining the current draw on
the AC input.

Take this flag into account when getting the ONLINE property of the AC
input, on PMICs where this flag is present.

Fixes: 7693b564 ("power: supply: add AC power supply driver for AXP813")
Cc: stable@vger.kernel.org
Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>