lib: utils/irqchip: Move per-hart data from fdt_plic to plic

The per-hart PLIC pointer is not really specific to FDT platforms. Move
it into the main driver and drop the extra wrapper functions.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

platform/template/platform.c

@@ -100,7 +100,7 @@ static int platform_irqchip_init(bool cold_boot)
 			return ret;
 	}
 
-	return plic_warm_irqchip_init(&plic);
+	return plic_warm_irqchip_init();
 }
 
 /*