msm: pil: Implement subsystem start/stop functions

Insert a shim implementation of the subsystem framework's start
and stop functions. For now, we call pil_get() and pil_put()
until all drivers are moved to start/stop functions.

Change-Id: Id25b0b748ebf942eae7e40e871b9693eeb50b38a
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>