dt-bindings: phy: qcom,qmp-pcie: add sc8280xp bindings

Add bindings for the PCIe QMP PHYs found on SC8280XP.

The PCIe2 and PCIe3 controllers and PHYs on SC8280XP can be used in
4-lane mode or as separate controllers and PHYs in 2-lane mode (e.g. as
PCIe2A and PCIe2B).

The configuration for a specific system can be read from a TCSR register.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>