libcutils: fix system-background tasks shown in top command

tasks in system-background cgroup will be shown as below:
 580   580 system   12  -8   1% S 190656K  19408K unk surfaceflinger  /system/bin/surfaceflinger

This patch fix this issue.

Change-Id: Ib39ff892010498548d7fbfb4021df62498acd033
Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com>
diff --git a/libcutils/sched_policy.cpp b/libcutils/sched_policy.cpp
index 73ca518..a9c061e 100644
--- a/libcutils/sched_policy.cpp
+++ b/libcutils/sched_policy.cpp
@@ -262,6 +262,8 @@
             *policy = SP_FOREGROUND;
         } else if (!strcmp(grpBuf, "foreground")) {
             *policy = SP_FOREGROUND;
+        } else if (!strcmp(grpBuf, "system-background")) {
+            *policy = SP_SYSTEM;
         } else if (!strcmp(grpBuf, "background")) {
             *policy = SP_BACKGROUND;
         } else if (!strcmp(grpBuf, "top-app")) {