ARM: dts: at91: Add the required 'atmel, rtt-rtc-time-reg' property

Add the required 'atmel,rtt-rtc-time-reg' property to the "rtt" nodes
of the board files that were missing it.

Signed-off-by: Sergiu Moga <sergiu.moga@microchip.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/all/20220304161159.147784-2-sergiu.moga@microchip.com


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