arm64: dts: r8a7795: Add RWDT node

This patch adds the RWDT device node for r8a7795.

Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>