arm64: dts: renesas: r8a7795: add thermal cooling management

Add nodes and properties for thermal cooling management support.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Acked-by: Eduardo Valentin <edubezval@gmail.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>