dtoc: Support reading a list of arguments

It is helpful to support a string or stringlist containing a list of
space-separated arguments, for example:

   args = "-n fred", "-a", "123";

This resolves to the list:

   -n fred -a 123

which can be passed to a program as arguments.

Add a helper to do the required processing.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/dtoc/fdt_util.py b/tools/dtoc/fdt_util.py
index d59ea2f..c82e774 100644
--- a/tools/dtoc/fdt_util.py
+++ b/tools/dtoc/fdt_util.py
@@ -184,6 +184,18 @@
         return [strval]
     return value
 
+def GetArgs(node, propname):
+    prop = node.props.get(propname)
+    if not prop:
+        raise ValueError(f"Node '{node.path}': Expected property '{propname}'")
+    if prop.bytes:
+        value = GetStringList(node, propname)
+    else:
+        value = []
+    lists = [v.split() for v in value]
+    args = [x for l in lists for x in l]
+    return args
+
 def GetBool(node, propname, default=False):
     """Get an boolean from a property