dt-bindings: PCI: Drop unneeded quotes

Cleanup bindings dropping unneeded quotes. Once all these are fixed,
checking for this can be enabled in yamllint.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230320233911.2920364-1-robh@kernel.org


Signed-off-by: Rob Herring <robh@kernel.org>