soc: mediatek: use of_device_get_match_data()

The usage of of_device_get_match_data() reduce the code size a bit.

Also, the only way to call pwrap_probe() is to match an entry in
of_pwrap_match_tbl[], so of_id cannot be NULL.

Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>