dt-bindings: mediatek: Add #reset-cells to mmsys system controller

The mmsys system controller exposes a set of memory client resets and
needs to specify the #reset-cells property in order to advertise the
number of cells needed to describe each of the resets.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210930103105.v4.2.I3f7f1c9a8e46be07d1757ddf4e0097535f3a7d41@changeid


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