thermal: rcar_thermal: add R8A77970 support

Add the R-Car V3M (R8A77970) SoC support to the R-Car gen2 thermal driver.
The hardware is the same as in the R-Car D3 (R8A77995) plus the CIVM status
register (we don't use).

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>