net: mdio: realtek-rtl9300: Add prefix to register field defines

net: mdio: realtek-rtl9300: Add prefix to register field defines

The current Realtek Otto MDIO driver has some define leftovers without
a SoC prefix. When adding new devices there will be an overlap for some
of them. Sort this out as follows:

- PHY_CTRL_CMD/PHY_CTRL_MMD_DEVAD/PHY_CTRL_MMD_REG are common for all
  series. Leave them as is but move them into a separate block.
- Add RTL9300 prefix to all other defines and adapt the callers.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://patch.msgid.link/20260610194145.4153668-3-markus.stockhausen@gmx.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>