dt-bindings: PCI: qcom,pcie-ipq6018: Move IPQ6018 and IPQ8074 Gen3 to dedicated schema

dt-bindings: PCI: qcom,pcie-ipq6018: Move IPQ6018 and IPQ8074 Gen3 to dedicated schema

Move IPQ6018 and IPQ8074 Gen3 (which is the same as in IPQ6018) PCIe
devices from qcom,pcie.yaml binding to a dedicated file to make
reviewing and maintenance easier.

New schema is equivalent to the old one with few changes:
 - Adding a required compatible, which is actually redundant.
 - Drop the really obvious comments next to clock/reg/reset-names items.
 - Disallow legacy/incomplete description with only one interrupt and
   expect exactly nine of them.
 - Do not require power domains on IPQ6018, because old binding already
   does not require them for IPQ8074 Gen3, devices are the same and
   in-tree DTS lacks power domains.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20251217-dt-bindings-pci-qcom-v2-6-873721599754@oss.qualcomm.com