dt-bindings: ARM: Mediatek: Add new document bindings of MT8192 clock

This patch adds the new binding documentation for system clock
and functional clock on Mediatek MT8192.

Signed-off-by: Chun-Jie Chen <chun-jie.chen@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210726105719.15793-2-chun-jie.chen@mediatek.com


Signed-off-by: Stephen Boyd <sboyd@kernel.org>