[RPi5] Activate NVMe PCIe Gen 3 Mode by default

[rootzoll]

Discussed in https://github.com/raspiblitz/raspiblitz/discussions/4394

[rootzoll]

For now we will keep "PCIe Gen 3" OFF to ensure most broad compatibility.

Even to to add it as an option later on could end up in a support nightmare if not done right. Because just adding a parameter to the raspiblitz.conf to have Gen3 active would then on every recover reanable gen3 and render a not campatible ssd unresponsive again.

If we add it as an option, it needs to be a more testing activation process - like activating it just for testing, make a reboot, check if nvme still shows up and only then write it to the config - it it fails revert the gen3 setting.

This could be done, but for now its not on high priority - pushed to later milestone for re-review.

[rootzoll]

also see: #4544