Adding this whitelist will add some PHY driver specific name in the phy API
core.
Will it be accepted? Is it not better to add a "legacy_default_timestamping"
boolean in the phy_device struct and set it for these 5 PHY drivers?
Then move on the default behavior to MAC default timestamping on the otehr
cases.

In the end, it is much the same thing. But if we really want this to
be legacy, not used by new drivers, putting it into the core will make
it harder for new drivers to set this bit and not get noticed during
review.

   Andrew