ARC: [SMP] cpumask not needed in IPI send path

The current IPI sending callstack needlessly involves cpumask.

   arch_send_call_function_single_ipi(cpu) / smp_send_reschedule(cpu)
      ipi_send_msg(cpumask_of(cpu))	--> [cpu to cpumask]
         plat_smp_ops.ipi_send(callmap)
            for_each_cpu(callmap)	--> [cpuask to cpu]
               do_plat_specific_ipi_PER_CPU

Given that current backends are not capable of 1:N IPIs, lets simplify
the interface for now, by keeping "a" cpu all along.

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
diff --git a/arch/arc/plat-arcfpga/smp.c b/arch/arc/plat-arcfpga/smp.c
index 91b5534..5e4fe95 100644
--- a/arch/arc/plat-arcfpga/smp.c
+++ b/arch/arc/plat-arcfpga/smp.c
@@ -88,13 +88,9 @@
 	smp_ipi_irq_setup(cpu, IDU_INTERRUPT_0 + cpu);
 }
 
-static void iss_model_ipi_send(void *arg)
+static void iss_model_ipi_send(int cpu)
 {
-	struct cpumask *callmap = arg;
-	unsigned int cpu;
-
-	for_each_cpu(cpu, callmap)
-		idu_irq_assert(cpu);
+	idu_irq_assert(cpu);
 }
 
 static void iss_model_ipi_clear(int cpu, int irq)