Add the standard cpuset nodes

These nodes are not meaningful in Microdroid, but added here in order to
satisfy the existing code that tries to put a PID to one of the cpusets.

Bug: 193118995
Test: run microdroid. Check if errors like the below are not shown:
couldn't write 152 to /dev/cpuset/system-background/tasks

Change-Id: Ibafb25355936ef21b6517c5707d093d25fc2d247
diff --git a/microdroid/init.rc b/microdroid/init.rc
index 36cddbb..614a5ed 100644
--- a/microdroid/init.rc
+++ b/microdroid/init.rc
@@ -48,6 +48,34 @@
     chmod 0666 /dev/binderfs/binder
     chmod 0666 /dev/binderfs/vndbinder
 
+    # Prepare cpusets that are pre-defined by Android. Inside Microdroid, these however don't mean
+    # much because the mapping from vCPUs to physical CPUs are quite flexible; a VM can be started
+    # with any number of vCPUs and we in general can't be sure that vCPU N is a big core or a little
+    # core. These nodes are provided just to satisfy the code which puts a PID to a specific cpuset.
+    mkdir /dev/cpuset/foreground
+    copy /dev/cpuset/cpus /dev/cpuset/foreground/cpus
+    copy /dev/cpuset/mems /dev/cpuset/foreground/mems
+    mkdir /dev/cpuset/background
+    copy /dev/cpuset/cpus /dev/cpuset/background/cpus
+    copy /dev/cpuset/mems /dev/cpuset/background/mems
+    mkdir /dev/cpuset/system-background
+    copy /dev/cpuset/cpus /dev/cpuset/system-background/cpus
+    copy /dev/cpuset/mems /dev/cpuset/system-background/mems
+
+    chown system system /dev/cpuset
+    chown system system /dev/cpuset/foreground
+    chown system system /dev/cpuset/background
+    chown system system /dev/cpuset/system-background
+    chown system system /dev/cpuset/tasks
+    chown system system /dev/cpuset/foreground/tasks
+    chown system system /dev/cpuset/background/tasks
+    chown system system /dev/cpuset/system-background/tasks
+
+    chmod 0664 /dev/cpuset/tasks
+    chmod 0664 /dev/cpuset/foreground/tasks
+    chmod 0664 /dev/cpuset/background/tasks
+    chmod 0664 /dev/cpuset/system-background/tasks
+
     # Start logd before any other services run to ensure we capture all of their logs.
     start logd