sh: Define HAVE_FUNCTION_TRACE_MCOUNT_TEST

Enable HAVE_FUNCTION_TRACE_MCOUNT_TEST and test the value of
function_trace_stop from our assembly code as opposed to using the
generic C function. This should optimise our mcount/ftrace code path.

Signed-off-by: Matt Fleming <matt@console-pimps.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>