dt-bindings: mailbox: mediatek,gce-mailbox: Add support for MT6795

Add a compatible string for the MT6795 Helio X10 SoC using MT8173
binding and add a header for the MT6795's GCE mailbox.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

dt-bindings: mailbox: mediatek,gce-mailbox: add mt8188 compatible name

Add mt8188 compatible name.

Signed-off-by: Elvis Wang <Elvis.Wang@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno<angelogioacchino.delregno@collabora.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

dt-bindings: mailbox: Convert mtk-gce to DT schema

Convert the mtk-gce mailbox binding to DT schema format.

During the conversion, the examples for client device/mutex nodes
were removed, as these are found in their respective bindings:
arm/mediatek/mediatek,mmsys.yaml for "mediatek,mt8173-mmsys"
soc/mediatek/mediatek,mutex.yaml for "mediatek,mt8173-disp-mutex"

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220921090006.37642-1-angelogioacchino.delregno@collabora.com
Signed-off-by: Rob Herring <robh@kernel.org>