[MTK] Update platforms

[cujomalainey]

MT8188 and MT8186 are in tree but missing on https://thesofproject.github.io/latest/platforms/index.html

Please update

[lgirdwood]

@thesofproject/mediatek fyi.

[kuanhsuncheng]

I will update ASAP. Thanks