Limit the WiFi PCIe link speed to Gen2 speed (500 MB/s), which is the
speed that the boot firmware has brought up the link at (and that
Windows uses).

This is specifically needed to avoid a large amount of link errors when
restarting the link during boot (but which are currently not reported).

This also appears to fix intermittent failures to download the ath11k
firmware during boot which can be seen when there is a longer delay
between restarting the link and loading the WiFi driver (e.g. when using
full disk encryption).

Fixes: 123b30a7 ("arm64: dts: qcom: sc8280xp-x13s: enable WiFi controller")
Cc: stable@vger.kernel.org      # 6.2
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20240223152124.20042-8-johan+linaro@kernel.orgSigned-off-by: Bjorn Andersson <andersson@kernel.org>