Documentation: ABI: power: Add missing newline at end of file

"git diff" says:

    \ No newline at end of file

after modifying the files.
Signed-off-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>