Documentation, split up rtc.txt into documentation and test file

This patch splits rtc.txt into two separate files, one for the
documentation itself, and the other for the rtctest.c file.  The rtctest
file is moved into the kernel tools/testing/selftests/timers directory.
This will make automated testing easier.  Note that the only difference in
the rtc.txt file is that the location of the rtctest.c file has changed.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Acked-by: Jonathan Corbet <corbet@lwn.net>
Acked-by: John Stultz <john.stultz@linaro.org>
Cc: corbet@lwn.net
Cc: rtc-linux@googlegroups.com
Cc: linux-doc@vger.kernel.org
Cc: a.zummo@towertech.it
Cc: prarit@redhat.com
Cc: john.stultz@linaro.org
Cc: shuahkh@osg.samsung.com
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>