net: phy: realtek: add RTL8224 pair order support

The RTL8224 has a register to configure a pair swap (from ABCD order to
DCBA) providing PCB designers more flexbility when wiring the chip. The
swap parameter has to be set correctly for each of the 4 ports before
the chip can detect a link.

After a reset, this register is (unfortunately) left in a random state,
thus it has to be initialized. On most of the devices the bootloader
does it once for all and we can rely on the value set, on some other it
is not and the kernel has to do it.

The MDI pair swap can be set in the device tree using the property
enet-phy-pair-order. The property is set to 0 to keep the default order
(ABCD), or 1 to reverse the pairs (DCBA).

Signed-off-by: Damien Dejean <dam.dejean@gmail.com>
Link: https://patch.msgid.link/20260318215502.106528-3-dam.dejean@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>