Add standby ports APIs to LowPowerStandbyManager

During Low Power Standby, most ports on the device will be blocked to
avoid unnecessary wakeups of the application processor.
Privileged apps can request ports to remain to continue to offer
essential functionality during Low Power Standby.

Bug: 234002812
Test: atest LowPowerStandbyControllerTest LowPowerStandbyTest
Change-Id: I67d57c9d020ed5e76eda0566dca57e0b4d4fecbd