ARM: dts: sam9x60: add rtt

Add RTT. Allong with it enable GBPR as it is requested by RTT.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/1591779936-18577-4-git-send-email-claudiu.beznea@microchip.com