arm64: dts: renesas: r8a77965: Add R-Car Gen3 thermal support

Based on previous work by Ryo Kataoka <ryo.kataoka.wt@renesas.com>.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
[simon: moved thermal node to preseve ordering of nodes by bus address]
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>