net: ethernet: mtk_wed: update mtk_wed_stop

Update mtk_wed_stop routine and rename old mtk_wed_stop() to
mtk_wed_deinit(). This is a preliminary patch to add Wireless Ethernet
Dispatcher reset support.

Co-developed-by: Sujuan Chen <sujuan.chen@mediatek.com>
Signed-off-by: Sujuan Chen <sujuan.chen@mediatek.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>