powerpc: Define NR_CPUS all the time

include/linux/threads.h defines a default value for CONFIG_NR_CPUS
but suggests the architectures should always define it.

So do it, when CONFIG_SMP is not selected set CONFIG_NR_CPUS to 1.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/afef0ec65a8ba8651bf4f6e4f4f08a8b6991dbfb.1620379469.git.christophe.leroy@csgroup.eu

arch/powerpc/platforms/Kconfig.cputype

@@ -476,9 +476,9 @@ config SMP
 	  If you don't know what to do here, say N.
 
 config NR_CPUS
-	int "Maximum number of CPUs (2-8192)"
-	range 2 8192
-	depends on SMP
+	int "Maximum number of CPUs (2-8192)" if SMP
+	range 2 8192 if SMP
+	default "1" if !SMP
 	default "32" if PPC64
 	default "4"