dt-bindings: phy: sc8280xp-qmp-pcie: Disallow bifurcation register on Purwa

dt-bindings: phy: sc8280xp-qmp-pcie: Disallow bifurcation register on Purwa

Neither of the two Gen4x4 PHYs found on Purwa supports bifurcation.
The PHY is however physically laid out as if it were to, since there
are two separate ports (A/B).

Split out a new if-then block to un-require the bifurcation register
handle to squash this warning:

purwa-iot-evk.dtb: phy@1bd4000 (qcom,x1p42100-qmp-gen4x4-pcie-phy): 'qcom,4ln-config-sel' is a required property

Fixes: 2e1ffd4c1805 ("dt-bindings: phy: qcom,qmp-pcie: Add X1P42100 PCIe Gen4x4 PHY")
Reported-by: Rob Herring <robh@kernel.org>
Closes: https://lore.kernel.org/linux-arm-msm/176857775469.1631885.16133311938753588148.robh@kernel.org/
Signed-off-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20260610-topic-purwa_phy_shutup_warning-v2-1-951c1fbfe9b2@oss.qualcomm.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>