sensors: ssc: Add restart interface for SLPI

Sensor Low Power Island (SLPI) is a DSP core integrated
into SDM/MSM to run sensor drivers and algorithms. User
space sensor daemon requires to restart the SLPI during
some of the use cases.
Add sysfs interface to do SLPI sub system restart from
user space sensor daemon.

Change-Id: Id5c16986aae4ac8a1fc1474fb542d36c70173a95
Signed-off-by: Ananda Kishore <kananda@codeaurora.org>