selftests/timers: Add nsleep-lat test from timetest suite

selftests/timers: Add nsleep-lat test from timetest suite

Adds my nanosleep latency test from the timetest suite.
This checks to make sure we don't see "unreasonable"
latencies (> 40ms) when calling nanosleep.

Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Tested-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>