ARM: mediatek: DT: Move reset controller constants into common location

By popular vote, the DT binding includes for reset controllers are located
in include/dt-bindings/reset/. Move the mediatek reset constants in there,
too, to avoid confusion.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>