healthimpl: wait for valid battery SOC in qti_healthd_board_init()

Currently, qti_healthd_board_init() only waits for the presence of
POWER_SUPPLY_CAPACITY property to ensure that battery power supply
is available before health HAL can start. However, on certain devices,
the presence of POWER_SUPPLY_CAPACITY alone wouldn't be sufficient.
Battery SOC published under this property would be available only
after a co-processor is booted up. To account in that delay and
the calculation of a valid battery SOC, increase the polling period
from 5 to 7.5 seconds. Also, make sure reading this property returns
a non-zero value so that when health HAL starts, it can read valid
values.

Change-Id: I79d413fe439f1e94c7b5d656ee14b9f5a5aa9703
1 file changed