net: dsa: realtek: support reset controller

Add support for resetting the device using a reset controller,
complementing the existing GPIO reset functionality (reset-gpios).

Although the reset is optional and the driver performs a soft reset
during setup, if the initial reset pin state was asserted, the driver
will not detect the device until the reset is deasserted.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>

net: dsa: realtek: migrate user_mii_bus setup to realtek_dsa

In the user MDIO driver, despite numerous references to SMI, including
its compatible string, there's nothing inherently specific about the SMI
interface in the user MDIO bus. Consequently, the code has been migrated
to the rtl83xx module. All references to SMI have been eliminated.

The MDIO bus id was changed from Realtek-<switch id> to the switch
devname suffixed with :user_mii, giving more information about the bus
it is referencing.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net: dsa: realtek: common rtl83xx module

Some code can be shared between both interface modules (MDIO and SMI)
and among variants. These interface functions migrated to a common
module:

- rtl83xx_lock
- rtl83xx_unlock
- rtl83xx_probe
- rtl83xx_register_switch
- rtl83xx_unregister_switch
- rtl83xx_shutdown
- rtl83xx_remove

The reset during probe was moved to the end of the common probe. This way,
we avoid a reset if anything else fails.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>