powerpc/perf: Quiet IMC PMU registration message

On a Power9 box we get a few screens full of these on boot. Drop
them to pr_debug.

  [    5.993645] nest_centaur6_imc performance monitor hardware support registered
  [    5.993728] nest_centaur7_imc performance monitor hardware support registered
  [    5.996510] core_imc performance monitor hardware support registered
  [    5.996569] nest_mba0_imc performance monitor hardware support registered
  [    5.996631] nest_mba1_imc performance monitor hardware support registered
  [    5.996685] nest_mba2_imc performance monitor hardware support registered

Signed-off-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Reviewed-by: Stewart Smith <stewart@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/perf/imc-pmu.c

@@ -1392,7 +1392,7 @@ int init_imc_pmu(struct device_node *parent, struct imc_pmu *pmu_ptr, int pmu_id
 	if (ret)
 		goto err_free_cpuhp_mem;
 
-	pr_info("%s performance monitor hardware support registered\n",
+	pr_debug("%s performance monitor hardware support registered\n",
 							pmu_ptr->pmu.name);
 
 	return 0;