power: supply: bq24735-charger: optionally poll the ac-detect gpio

If the ac-detect gpio does not support interrupts, provide a fallback
to poll the gpio at a configurable interval.

Signed-off-by: Peter Rosin <peda@axentia.se>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sre@kernel.org>