dt-bindings: PCI: qcom: Add MSM8998 specific compatible

Add new compatible for MSM8998 (compatible with MSM8996) to allow further
customizing if needed and to accurately describe the hardware.

Link: https://lore.kernel.org/r/20230106081203.14118-2-krzysztof.kozlowski@linaro.org


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rob Herring <robh@kernel.org>