thermal: mediatek: Prepare to add support for other platforms

It is known that Mediatek owns two thermal systems, which only differ
in the way of reading calibration data and converting temperature.
MT8173, MT8183, MT2701 and MT2712 belongs to version 1 thermal
system, and MT7622 belongs to version 2.

In order to handle both systems, the suffix _V1 is appended to the
current code, and then the second patch will add _V2 functions with
the same purpose but different implementation.

Signed-off-by: Henry Yen <henry.yen@mediatek.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Tested-By: Frank Wunderlich <frank-w@public-files.de>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/1588238074-19338-2-git-send-email-henry.yen@mediatek.com