Changes in v2:

v2:
1) Delete patch 'stmmac: dwmac-mediatek: add support for mt8188' as
Krzysztof Kozlowski's comment.
2) Update patch 'dt-bindings: net: mediatek-dwmac: add support for
mt8188' as Krzysztof Kozlowski's comment.
3) Add clk_csr property to fix warning ('clk_csr' was unexpected)
reported by running 'make dtbs_check'.

v1:
1) Add ethernet driver entry for mt8188.
2) Add binding document for ethernet on mt8188.