dt-bindings: phy: qcom,sc8280xp-qmp-pcie-phy: document PHY AUX clock on SM8[456]50 SoCs

The PCIe Gen4x2 PHY found in the SM8[456]50 SoCs have a second clock named
"PHY_AUX_CLK" which is an input of the Global Clock Controller (GCC) which
is muxed & gated then returned to the PHY as an input.

Document the clock IDs to select the PIPE clock or the AUX clock,
also enforce a second clock-output-names and a #clock-cells value of 1
for the PCIe Gen4x2 PHY found in the SM8[456]50 SoCs.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20240322-topic-sm8x50-upstream-pcie-1-phy-aux-clk-v2-1-3ec0a966d52f@linaro.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>