refine script for pi.

@@ -300,8 +300,8 @@ function OSX_prepare()
 OSX_prepare; ret=$?; if [[ 0 -ne $ret ]]; then echo "OSX prepare failed, ret=$ret"; exit $ret; fi
 
 # by winlin, disable other system.
-if [[ $OS_IS_UBUNTU = NO && $OS_IS_CENTOS = NO && $SRS_EMBEDED_CPU = NO ]]; then
-    echo "only support Centos and Ubuntu, actual is `uname -s`"
+if [[ $OS_IS_UBUNTU = NO && $OS_IS_CENTOS = NO && SRS_PI = NO && $SRS_EMBEDED_CPU = NO ]]; then
+    echo "only support Centos/Ubuntu/RaspberryPi, actual is `uname -s`"
     exit 1
 fi