drivers: nxp_enet: Deprecate ETH_MCUX

Deprecate ETH_MCUX, by:

- Marking it as DEPRECATED in Kconfig, obviously.
- Unmarking the new driver as experimental.
- Putting the new and old drivers in the same folder.
- Reworking the menu appearance of the driver selection.
  Note that technically now it is possible to choose the wrong
  driver than what is enabled in DT, this is intentional, but
  the correct one will obviously be enabled by default.
- Convert all sample overlays to the new Kconfigs. This was
  part of the motivation for the shared overlays, as it was
  causing twister/CI logs to look ugly and misleading due
  to Kconfig warnings.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>