ARM: shmobile: r8a7791 dtsi: Add CPG/MSTP Clock Domain

Add an appropriate "#power-domain-cells" property to the cpg_clocks
device node, to create the CPG/MSTP Clock Domain.

Add "power-domains" properties to all device nodes for devices that are
part of the CPG/MSTP Clock Domain and can be power-managed through an
MSTP clock.  This applies to most on-SoC devices, which have a
one-to-one mapping from SoC device to DT device node.  Notable
exceptions are the "display" and "sound" nodes, which represent multiple
SoC devices, each having their own MSTP clocks.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>