lib: utils/irqchip: Initialize all matching irqchip DT nodes

We can have multiple matching DT nodes of the same FDT irqchip
driver so in this case we should call cold_init() for all matching
DT nodes instead of just first matching DT node.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>