dt-bindings: ARM: MediaTek: Add new document bindings of MT8186 clock

This patch adds the new binding documentation for system clock
and functional clock on MediaTek MT8186.

Signed-off-by: Chun-Jie Chen <chun-jie.chen@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220409132251.31725-2-chun-jie.chen@mediatek.com


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