drivers: soc: atmel: move sam9x60 under its own config flag

Move SAM9X60 under its own config flag.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/1575035505-6310-5-git-send-email-claudiu.beznea@microchip.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>