dt-bindings: mediatek: Document MT6795 system controllers bindings

Document the MediaTek Helio X10 (MT6795) bindings for the apmixedsys,
infracfg, topckgen, pericfg and mmsys system controllers.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220921091455.41327-2-angelogioacchino.delregno@collabora.com


Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>