dt-bindings: clock: mediatek: document clk bindings for mediatek mt7986 SoC

This patch adds the binding documentation for topckgen, apmixedsys,
infracfg, and ethernet subsystem clocks.

Signed-off-by: Sam Shih <sam.shih@mediatek.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211217121148.6753-2-sam.shih@mediatek.com


Reviewed-by: Ryder Lee <ryder.lee@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>