dt-bindings: timer: mediatek: Convert to json-schema

Convert the MediaTek SoC timer txt binding to json-schema.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220929122901.614315-3-angelogioacchino.delregno@collabora.com


[robh: Add mt8365 compatible, drop duplicate mediatek,mt6795-systimer, drop quotes]
Signed-off-by: Rob Herring <robh@kernel.org>