power: supply: sc27xx: Add suspend/resume interfaces

Add fuel gauge platform suspend and resume interfaces. In suspend state,
we should enable the low voltage and coulomb counter threshold interrupts
to wake up system to calibrate the battery capacity in lower voltage stage.

Signed-off-by: Yuanjiang Yu <yuanjiang.yu@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>