ARM: dts: r7s9210: Initial SoC device tree

Basic support for the RZ/A2 (R7S9210) SoC.

Signed-off-by: Chris Brandt <chris.brandt@renesas.com>
Reviewed-by: Ulrich Hecht <uli+renesas@fpond.eu>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>