ARM: dts: r8a7791: Use SYSC "always-on" PM Domain

Hook up all devices that are part of the CPG/MSTP Clock Domain to the
SYSC "always-on" PM Domain, for a more consistent device-power-area
description in DT.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>