dt-bindings: arm: mediatek: Add mt8186 pericfg compatible

Add mt8186 pericfg compatible to binding document.

Signed-off-by: Allen-KH Cheng <allen-kh.cheng@mediatek.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220520122217.30716-2-allen-kh.cheng@mediatek.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>