ARM: shmobile: r8a73a4: add thermal driver support

You can get current thermal by
> cat /sys/class/thermal/thermal_zone?/temp

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>