audio: Add DriverInterface::start method

This method is used to bring out the hardware from standby.
It replaces the ad hoc 'exitStandby' method in StreamUsb.

Streamlined StreamUsb code to avoid locking during transfers.

Updated StreamRemoteSubmix to use 'start'.

Added extra checks to StreamStub to ensure that 'init/shutdown'
and 'standby/start' methods are called as expected. This allows
removing extra checks from non-stub stream implementations.

Bug: 205884982
Test: atest VtsHalAudioCoreTargetTest
Change-Id: I3615a7ca99cb4f1e149dcbfbc912f2ed58fb033f