ARC: Allow SMP kernel to build/boot on UP-only infrastructure

In light of recent SNAFU with SMP build, allow simple platform to build
as SMP but run UP.

* Remove the dependence on simulation SMP extension to enable quick
  build/test iterations of SMP kernel.

* In absence of platform SMP registration, prevent the NULL smp feature
  name from borkign the system

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
diff --git a/arch/arc/kernel/smp.c b/arch/arc/kernel/smp.c
index dcd317c..d01df0c 100644
--- a/arch/arc/kernel/smp.c
+++ b/arch/arc/kernel/smp.c
@@ -101,7 +101,7 @@
 
 const char *arc_platform_smp_cpuinfo(void)
 {
-	return plat_smp_ops.info;
+	return plat_smp_ops.info ? : "";
 }
 
 /*