selftests/ftrace: mark irqsoff_tracer.tc test as unresolved if the test module does not exist

The UNRESOLVED state is much more apporiate than the UNSUPPORTED state
for the absence of the test module, as it matches "test was set up
incorrectly" situation in the README file.

A possible scenario is that the function was enabled (supported by the
kernel) but the module was not installed properly, in this case we
cannot call this as UNSUPPORTED.

This change also make it consistent with other module-related tests
in ftrace.

Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>