dsp: Add restart interface for adsp

User space sensor daemon requires to restart the audio dsp
during some of the sensors usecases. Add sysfs interface to
do adsp subsystem restart from user space sensor daemon.

Change-Id: I07c78892cb6e6f99ae93c04eddbc321681b52a70
Signed-off-by: Shaikh Shadul <sshadu@codeaurora.org>