dt-bindings: PCI: qcom: x1e80100: Make the MHI reg region mandatory

dt-bindings: PCI: qcom: x1e80100: Make the MHI reg region mandatory

All PCIe controllers found on X1E80100 have MHI register region.
So change the schema to reflect that.

Fixes: 692eadd51698 ("dt-bindings: PCI: qcom: Document the X1E80100 PCIe Controller")
Link: https://lore.kernel.org/linux-pci/20240605-x1e80100-pci-bindings-fix-v2-1-c465e87966fc@linaro.org
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>