dt-bindings: PCI: qcom,pcie-sa8775p: Move SA8775p to dedicated schema

dt-bindings: PCI: qcom,pcie-sa8775p: Move SA8775p to dedicated schema

Move SA8775p PCIe devices from qcom,pcie.yaml binding to a dedicated file
to make reviewing easier.

This creates equivalent schema file, except:
 - Missing required compatible which is actually redundant.
 - Expecting eight MSI interrupts, instead of only one, which was
   incomplete hardware description.

Link: https://lore.kernel.org/linux-pci/20240205-dt-bindings-pci-qcom-split-continued-v1-3-c333cab5eeea@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>