net: enetc: add pre-boot initialization for i.MX94 switch

net: enetc: add pre-boot initialization for i.MX94 switch

Before probing the NETC switch driver, some pre-initialization needs to
be set in NETCMIX and IERB to ensure that the switch can work properly.
For example, i.MX94 NETC switch has three external ports and each port
is bound to a link. And each link needs to be configured so that it can
work properly, such as I/O variant and MII protocol.

In addition, the switch port 2 (MAC 2) and ENETC 0 (MAC 3) share the same
parallel interface, they cannot be used at the same time due to the SoC
constraint. And the MAC selection is controlled by the mac2_mac3_sel bit
of EXT_PIN_CONTROL register. Currently, the interface is set for ENETC 0
by default unless the switch port 2 is enabled in the DT node.

Like ENETC, each external port of the NETC switch can manage its external
PHY through its port MDIO registers. And the port can only access its own
external PHY by setting the PHY address to the LaBCR[MDIO_PHYAD_PRTAD].
If the accessed PHY address is not equal to LaBCR[MDIO_PHYAD_PRTAD], then
the MDIO access initiated by port MDIO will be invalid.

Signed-off-by: Wei Fang <wei.fang@nxp.com>
Link: https://patch.msgid.link/20260518082506.1318236-4-wei.fang@nxp.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>