selftests: timers: move PIE tests out of rtctest

Since commit 6610e089 ("RTC: Rework RTC code to use timerqueue for
events"), PIE are completely handled using hrtimers, without actually using
any underlying hardware RTC.

Move PIE testing out of rtctest. It still depends on the presence of an RTC
(to access the device file) but doesn't depend on it actually working.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>