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/include/asm/smp.h b/arch/arc/include/asm/smp.h
index 5d06eee..3845b9e 100644
--- a/arch/arc/include/asm/smp.h
+++ b/arch/arc/include/asm/smp.h
@@ -59,7 +59,15 @@
 /* TBD: stop exporting it for direct population by platform */
 extern struct plat_smp_ops  plat_smp_ops;
 
-#endif  /* CONFIG_SMP */
+#else /* CONFIG_SMP */
+
+static inline void smp_init_cpus(void) {}
+static inline const char *arc_platform_smp_cpuinfo(void)
+{
+	return "";
+}
+
+#endif  /* !CONFIG_SMP */
 
 /*
  * ARC700 doesn't support atomic Read-Modify-Write ops.