ARM: dts: lan966x: add all flexcom usart nodes

Add all the remaining usart nodes for the flexcom block. Although the
DMA channels are specified, DMA is not enabled by default because break
detection doesn't work with DMA.

Keep the nodes disabled by default.

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/20220502224127.2604333-5-michael@walle.cc


Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>