dt-bindings: display: mediatek: add dsi reset optional property

Update device tree binding documentation for the dsi to add the optional
property to reset the dsi controller.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210930103105.v4.3.Ifec72a83f224b62f24cfc967edfe78c5d276b2e3@changeid


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>