arm: tracing: disable tracing for the timer clock functions

The function graph tracer causes a kernel crash when enabled. This is
because the counter_get_cntvct_cp15 and the trace_local_clock functions
call each other recursively causing a kernel stack overflow. Fix this
by annotating the timer clock functions with notrace.

Change-Id: I89864012cf98054265ac8c5ed1fb4870ca00c5a4
CRs-Fixed: 525920
Signed-off-by: Pushkar Joshi <pushkarj@codeaurora.org>