Scale stack manager start timeouts with sys prop

As with the AdapterState state machine, the stack manager needs to scale
it's timeouts in accordance with ro.hw_timeout_multiplier, to give slow
hardware (e.g. the RISC-V emulator) time to reliably start the stack.

Bug: 308798575
Test: Verified 10 of 10 Bluetooth startups of RISC-V CF on slow machine.
Test: m libbluetooth_gd
Change-Id: I2427187e388307c5ef386b8e592afb033392e1d5