soc.py: ethernet: use phy_cd name from phy

[maass-hamburg]

use phy_cd name directly from phy.

Signed-off-by: Fin Maaß [email protected]

[enjoy-digital]

Thanks @maass-hamburg, would you mind describing the context/use-case to think about it and review it with this in mind?

[maass-hamburg]

It uses the same logic, as the part a little bit under it at with_timing_constraints, to get the phy names. This can be very useful, when you want to use than one phy (multiple instances), specificly when each phy has its own ClockDomains, like here: enjoy-digital/liteeth#181. There I numbered the ClockDomain Names, so they would not replace each other.