irqchip/gic: Only set the EOImodeNS bit for the root controller

EOImode1 is only used for the root controller and hence only the root
controller uses the eoimode1 functions for handling interrupts. However,
if the root controller supports EOImode1, then the EOImodeNS bit will be
set for all GICs, enabling EOImode1. This is not what we want and this
causes interrupts on non-root GICs to only be dropped in priority but
never deactivated. Therefore, only set the EOImodeNS bit for the root
controller.

Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>