Target: add read_tree_values and read_tree_values_flat

Add two new methods to target that allow querying values of all sysfs
nodes in a sub-directory structure all at once. The difference is that
read_tree_values_flat returns a flat dict of path->value mappings;
read_tree_values returns a nested dict structure that mimics the
scanned sub-directories tree.

devlib/bin/scripts/shutils.in

@@ -195,6 +195,22 @@ cgroups_freezer_set_state() {
     exit 1
 }
 
+################################################################################
+# Misc
+################################################################################
+
+read_tree_values() {
+    PATH=$1
+    MAXDEPTH=$2
+
+    PATHS=$($BUSYBOX find $PATH -follow -maxdepth $MAXDEPTH)
+    if [ ${#PATHS[@]} -eq 0 ]; then
+        echo "ERROR: '$1' does not exist"
+    else
+        $BUSYBOX grep -s '' $PATHS
+    fi
+}
+
 ################################################################################
 # Main Function Dispatcher
 ################################################################################
@@ -236,6 +252,9 @@ cgroups_freezer_set_state)
 ftrace_get_function_stats)
     ftrace_get_function_stats
     ;;
+read_tree_values)
+	read_tree_values $*
+    ;;
 *)
     echo "Command [$CMD] not supported"
     exit -1