ARM: dts: r8a7744: Add thermal device to DT

This patch instantiates the thermal sensor module with thermal-zone
support.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>