init: start audio rpc daemon early to improve performance

Audio HAL initialization relies on rpc daemon to load
dynamic libs, if daemon is not ready when HAL tries
to load libs, HAL has to wait until that finished.
Start this daemon early can smooth boot up of audio HAL
process, as this can save time for dynamic libs loading.

Change-Id: Id05ffc46fab812a718b6cb601e0610974b123679