selftests: timers: Convert nsleep-lat test to generate KTAP output

Currently the nsleep-lat test does not produce KTAP output but rather a
custom format. This means that we only get a pass/fail for the suite, not
for each individual test that the suite does. Convert to using the standard
kselftest output functions which result in KTAP output being generated.

Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>