scripts: devicetree.py: get alternate labels from dt

Allow use of new element of dtc grammar called overriding nodes:
i2cexp: &i2c2  {};

It allows a node to assign an alternate label to a node that
could be generic and used for adapter boards.
This commit is a derivative of a dtc commit from dtc v1.4.2 [1]

[1] https://bit.ly/2GFLLOa

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>

scripts/dts/devicetree.py

@@ -48,15 +48,23 @@ def parse_node_name(line):
         addr = None
 
     if ':' in line:
-        label, name = line.split(':')
+        if len(line.split(':')) == 3:
+            alt_label, label, name = line.split(':')
+        else:
+            label, name = line.split(':')
+            alt_label = None
     else:
         name = line
         label = None
+        alt_label = None
 
     if addr is None:
-        return label, name.strip(), None, None
+        return label, name.strip(), None, None, None
 
-    return label, name.strip(), addr, int(addr, 16)
+    if alt_label is None:
+        return label, name.strip(), addr, int(addr, 16), None
+
+    return label, name.strip(), addr, int(addr, 16), alt_label
 
 def parse_values_internal(value, start, end, separator):
     out = []
@@ -142,7 +150,7 @@ def build_node_name(name, addr):
     return '%s@%s' % (name, addr.strip())
 
 def parse_node(line, fd):
-    label, name, addr, numeric_addr = parse_node_name(line)
+    label, name, addr, numeric_addr, alt_label = parse_node_name(line)
 
     node = {
         'label': label,
@@ -152,6 +160,9 @@ def parse_node(line, fd):
         'props': {},
         'name': build_node_name(name, addr)
     }
+    if alt_label:
+        node['alt_name'] = alt_label
+
     while True:
         line = fd.readline()
         if not line: