Add the MDIO controller nodes. The integrated PHYs are connected to the
second controller. This controller also takes care of the resets of the
integrated PHYs, thus it has two memory regions. The first controller
is routed to the external MDIO/MDC pins.

By default, they are disabled.
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Tested-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220502224127.2604333-10-michael@walle.ccSigned-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>