ARM: dts: at91: sam9x60ek: Add DBGU compatibles to uart1

Maintain consistency among the compatibles of the serial nodes of
sam9x60ek and highlight the incremental characteristic of its serial
IP's by making sure that all serial nodes contain both the sam9x60
and sam9260 usart/dbgu compatibles.

Signed-off-by: Sergiu Moga <sergiu.moga@microchip.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220913142205.162399-3-sergiu.moga@microchip.com