ARM: shmobile: r8a73a4 dtsi: Add PM domain support

Add a device node for the System Controller, with subnodes that
represent the hardware power area hierarchy.
Hook up all devices to their respective PM domains.

Add a minimal device node for the Coresight-ETM hardware block, and
hook it up to the D4 PM domain, so the R-Mobile System Controller
driver can keep the domain powered, until the new Coresight code
handles runtime PM.

The System Controller is also used by the R-Mobile Reset driver, which
can now restart the system.

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