documentation: Move power-related files to Documentation/power/

Move 00-INDEX entries to power/00-INDEX (and add entry for
pm_qos_interface.txt).

Update references to moved filenames.

Fix some trailing whitespace.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Len Brown <len.brown@intel.com>