net: mediatek: use a struct to cover variations of all SoCs

net: mediatek: use a struct to cover variations of all SoCs

Using a single soc id to control different initialization and TX/RX flow
for all SoCs is not extensible if more hardware variations are added in
the future.

This patch introduces a struct to replace the original mtk_soc to allow
the driver be able handle newer hardwares.

Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>