arm64: dts: renesas: r8a779f0: Use proper labels for thermal zones

arm64: dts: renesas: r8a779f0: Use proper labels for thermal zones

The documentation provides information about the placement of the zones,
so that can be used for more descriptive labels.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20230209200735.3882-1-wsa+renesas@sang-engineering.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>