device-pine64-pinephone: shutdown on critical battery (MR 2193)

The PMIC AXP803 sends an interrupt to the A64 CPU when the
battery is critical low. This wakes up the phone at ~10%
battery level, but UPower wasn't configured to add upon
this interrupt as the action level was way lower.
Therefore, the PMIC performed a hard shutdown when the
battery level dropped further, which may cause data loss.