openrisc: add NR_CPUS Kconfig default value

The build system now expects that NR_CPUS is defined.

Follow 4cbbbb4 ("microblaze: Fix missing NR_CPUS in menuconfig")

Signed-off-by: Stafford Horne <shorne@gmail.com>
diff --git a/arch/openrisc/Kconfig b/arch/openrisc/Kconfig
index 489e7f9..691e1af 100644
--- a/arch/openrisc/Kconfig
+++ b/arch/openrisc/Kconfig
@@ -98,6 +98,9 @@
 	  Select this if your implementation has a hardware divide instruction
 endmenu
 
+config NR_CPUS
+	int
+	default "1"
 
 source kernel/Kconfig.hz
 source kernel/Kconfig.preempt