ARM: at91/board-dt: remove AIC irq domain from board file

Adding of irqdomain in AIC code make the specification
of the irq domain in board file useless.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>