soc: mediatek: reuse regmap_read_poll_timeout helpers

Reuse the common helpers regmap_read_poll_timeout provided by Linux core
instead of an open-coded handling.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Weiyi Lu <weiyi.lu@mediatek.com>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>