cpuidle: teo: Use kerneldoc documentation in admin-guide

There are two descriptions of the TEO (Timer Events Oriented) cpuidle
governor in the kernel source tree, one in the C file containing its
code and one in cpuidle.rst which is part of admin-guide.

Instead of trying to keep them both in sync and in order to reduce
text duplication, include the governor description from the C file
directly into cpuidle.rst.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>