ARM: dts: r8a7794: Add reset control properties

Add properties to describe the reset topology for on-SoC devices:
  - Add the "#reset-cells" property to the CPG/MSSR device node,
  - Add resets and reset-names properties to the various device nodes.

This allows to reset SoC devices using the Reset Controller API.

Note that resets usually match the corresponding module clocks.
Exceptions are:
  - The audio module has resets for the Serial Sound Interfaces only,
  - The display module has only a single reset for all DU channels, but
    adding reset properties for the display is postponed.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>