dt-bindings: display: mediatek: dpi: Allow specifying resets

Even though the DPI IP has a reset bit on all MediaTek SoCs, it
is optional, and has always been unused until MT8195; specifically:
on older SoCs, like MT8173, the reset bit is located in MMSYS, and
on newer SoCs, like MT8195, it is located in VDOSYS.

For this reason, allow specifying the resets and reset-names on
all MediaTek SoCs.

Those properties are optional because there are multiple ways to
reset this IP and the reset lines in MM/VDO are used only if the
IP cannot perform warm-reset.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>