net: mdio: realtek-rtl9300: Add support for RTL931x

net: mdio: realtek-rtl9300: Add support for RTL931x

The MDIO driver has been prepared for multiple device support. Add all
required bits for the RTL931x (aka mango) series. This is straightforward
but some things are worth to be mentioned.

- In contrast to RTL930x the I/O register has the input/output fields
  swapped. Upper 16 bits are for read/outputs, and the lower 16 bits
  are for write/inputs.
- The supported "pages" are 8192 and thus the raw page is 8191
- The devices support up to 56 ports. Thus the MAX_PORTS definition
  is increased by this commit.
- There are multiple global SMI controller registers with a different
  layout from RTL930x devices. Therefore a separate setup_controller()
  callback is added.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://patch.msgid.link/20260610194145.4153668-6-markus.stockhausen@gmx.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>