driver: net: fm: add DM ETH support

Probe the FMan MACs based on the device tree while
retaining the legacy code/functionality.
One notable change introduced here is that, for DM_ETH,
the name of the interfaces is corrected to the fmX-macY
format, that avoids the referral to the MAC block names
which were incorrect for FMan v3 devices (i.e. DTSEC,
TGEC) and had weird formatting (i.e. FM1@DTSEC6, FM1@TGEC1).
The legacy code is left unchanged in this respect.

Signed-off-by: Madalin Bucur <madalin.bucur@oss.nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>