power: supply: max17040: Support soc alert

max17048 and max17049 support SOC alerts (interrupts when battery
capacity changes by +/- 1%). At the moment the driver polls for changes
every second. Using the alerts removes the need for polling.

Signed-off-by: Iskren Chernev <iskren.chernev@gmail.com>
Tested-by: Jonathan Bakker <xc-racer2@live.ca>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>