net: phy: adin: add support MDI/MDIX/Auto-MDI selection

net: phy: adin: add support MDI/MDIX/Auto-MDI selection

The ADIN PHYs support automatic MDI/MDIX negotiation. By default this is
disabled, so this is enabled at `config_init`.

This is controlled via the PHY Control 1 register.
The supported modes are:
  1. Manual MDI
  2. Manual MDIX
  3. Auto MDIX - prefer MDIX
  4. Auto MDIX - prefer MDI

The phydev mdix & mdix_ctrl fields include modes 3 & 4 into a single
auto-mode. So, the default mode this driver enables is 4 when Auto-MDI mode
is used.

When detecting MDI/MDIX mode, a combination of the PHY Control 1 register
and PHY Status 1 register is used to determine the correct MDI/MDIX mode.

If Auto-MDI mode is not set, then the manual MDI/MDIX mode is returned.
If Auto-MDI mode is set, then MDIX mode is returned differs from the
preferred MDI/MDIX mode.
This covers all cases where:
  1. MDI preferred  & Pair01Swapped   == MDIX
  2. MDIX preferred & Pair01Swapped   == MDI
  3. MDI preferred  & ! Pair01Swapped == MDIX
  4. MDIX preferred & ! Pair01Swapped == MDI

The preferred MDI/MDIX mode is not configured via SW, but can be configured
via HW pins. Note that the `Pair01Swapped` is the Green-Yellow physical
pairs.

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: David S. Miller <davem@davemloft.net>