dt-bindings: PCI: qcom-ep: Define clocks per platform

In preparation for adding the bindings for future SoCs, define the
clocks per platform.

Link: https://lore.kernel.org/r/20220914075350.7992-11-manivannan.sadhasivam@linaro.org


Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>