csky: Set CONFIG_NR_CPU 4 as default

The C860 processors support 4 cores smp for maximum, so set NR_CPU
to 4 as default
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Cc: Arnd Bergmann <arnd@arndb.de>

arch/csky/Kconfig

@@ -279,7 +279,7 @@ config NR_CPUS
 	int "Maximum number of CPUs (2-32)"
 	range 2 32
 	depends on SMP
-	default "2"
+	default "4"
 
 config HIGHMEM
 	bool "High Memory Support"