tests: Fix coherence of timeout spin lock

Spin locks must be in coherent memory for cavs. Initially this variable
was at the compilation unit scope but warnings about it being unused
from a twister run lead me to move it to be in the ifdef scope in the
function.

Move it back into the compilation units scope and wrap it in an
ifdef to ensure its not labeled as unused.

Signed-off-by: Tom Burdick <thomas.burdick@intel.com>