drivers/thermal/rcar_gen3_thermal: introduce 'info' structure

More items to describe the TSCs are needed soon, so encapsulate the
current 'ths_tj_1' item into a struct.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20230511192220.7523-2-wsa+renesas@sang-engineering.com