Add support for start/load "busy" error code

This change allows the soundtrigger HAL to return -EBUSY on start and
load and adds proper handling in the middleware.

Test: atest SoundTriggerMiddlewareImplTest SoundHw2CompatTest
Bug: 178722883
Change-Id: I7d34d5ec076486527b5540da4cd7f18ca362260b