arm64: dts: qcom: sa8775p: Remove max link speed property for PCIe EP

The maximum link speed was previously restricted to Gen3 due to the
absence of Gen4 equalization support in the driver.

As Gen4 equalization is already supported by the PCIe controller
driver, remove the max-link-speed property.

Signed-off-by: Mrinmay Sarkar <mrinmay.sarkar@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250617-update_phy-v5-2-2df83ed6a373@quicinc.com


Signed-off-by: Bjorn Andersson <andersson@kernel.org>