power: supply: max17040: Add IRQ handler for low SOC alert

According datasheet max17040 has a pin for alert host for low SOC.
This pin can be used as external interrupt, so we need to check for
interrupts assigned for device and handle it.

In handler we are checking and storing fuel gauge registers values
and send an uevent to notificate user space, so user space can decide
save work or turn off since the alert demonstrate that the battery may
no have the power to keep the system turned on for much longer.

Signed-off-by: Matheus Castello <matheus@castello.eng.br>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>