dt-bindings: PCI: mediatek,mt7621-pcie: Switch from deprecated pci-bus.yaml

dt-bindings: PCI: mediatek,mt7621-pcie: Switch from deprecated pci-bus.yaml

dtschema package with core schemas deprecated pci-bus.yaml schema in
favor of individual schemas per host, device and pci-pci.

Switch Mediatek MT7621 PCIe host bridge binding to this new schema.

This requires dtschema package newer than v2024.02 to work fully.
v2024.02 will partially work: with a warning.

Link: https://lore.kernel.org/linux-pci/20240413151617.35630-4-krzysztof.kozlowski@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>