net: dwc_eth_qos: remove use of DWC_NET_PHYADDR

Only two boards in the tree set the macro DWC_NET_PHYADDR. Both have
CONFIG_DM_ETH_PHY=y, so should set the phy address in DT if necessary.

The imx8mp_evk does set the correct address in device tree.

The other board seems to be a copy-paste-adapt from an old
version of the imx8mp_evk config header, given the "#ifdef
CONFIG_DWC_ETH_QOS" block that has been removed from imx8mp_evk header
in commit 127fb454. Its device tree doesn't even enable (i.e., set
'status = "okay"') the &eqos node. But the other ethernet device,
&fec, does get enabled, and does have a phy sitting at address 4 (and
it also has a corresponding legacy #define CONFIG_FEC_MXC_PHYADDR
4). So I believe it should be completely safe to remove it from there
as well.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
[trini: Re-apply to top of tree, update imx93_evk.h]
Signed-off-by: Tom Rini <trini@konsulko.com>