irqchip/atmel-aic5: Add support for sam9x60 irqchip

Add support for SAM9X60 irqchip.

Signed-off-by: Sandeep Sheriker Mallikarjun <sandeepsheriker.mallikarjun@microchip.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/1568026835-6646-1-git-send-email-claudiu.beznea@microchip.com

[claudiu.beznea@microchip.com: update aic5_irq_fixups[], update
 documentation]