ARM: dts: lan966x: add support for pcb8290

Add basic support for pcb8290. It has 2 lan8814 phys(each phy is a
quad-port) on the external MDIO bus and no SFP ports.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220825065135.1075049-1-horatiu.vultur@microchip.com