msm: ultrasound: add support for aDSP Sub-System Restart

Add handling of RESET_EVENTS message from APR, which indicates
aDSP sub-system restart has begun.

Add a new internal state, USF_ADSP_RESTART_STATE, for this
scenario.

Change-Id: Ic1a78f28e63ca1f8b985373cf2bd7a089ae63978
Signed-off-by: Lior Barenboim <liorb@codeaurora.org>