core_ctl: Add refcounting to boost api

More than one client may call the core_ctl_set_boost api. Add support
for this.
Also add a new trace event that is emitted when this api is called.

Change-Id: Iad0a9fc45f1ce87433995e8e549bfca80e8b9cb2
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>