ARM: dts: at91: add conflict note for d3

Pin feeding d3 led may be in conflict with EBI CS0, USART2 CTS.
Add a note for this.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20210727074006.1609989-2-claudiu.beznea@microchip.com