[AAE Power Mgt] Allow Suspend to RAM without triggering Garage Mode

The Vehicle HAL can tell us to shut down immediately, but it cannot
tell us to suspend immediately. Add that capability.

This capability will be needed when the VHAL initiates a Silent
Boot and then asks for suspension. In this case, we do not want
to postpone the suspension by entering Garage Mode.

Bug: 134521909
Test: Added CarPowerManagementTest.testSleepImmediateEntry()
Test: Added CarPowerManagementServiceTest.testSleepImmediately()
Change-Id: I8190d16cb6faa15672ec3d61f126f6d283d1189e