mfd: axp20x-i2c: Add i2c-ids to fix module auto-loading

The i2c subsys does not load modules by compatible, only by
i2c-id, with e.g. a modalias of: "i2c:axp209".

Populate the axp20x_i2c_id[] table with supported ids, so that
module auto-loading will work.

Reported-by: Dennis Gilmore <dennis@ausil.us>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>