tools/pydfu.py: Add support for multiple memory segments.

Segments are separated by / and begin with the memory address.  This
follows how the ST DFU tool works.

tools/pydfu.py

@@ -394,10 +394,11 @@ def get_memory_layout(device):
     intf = cfg[(0, 0)]
     mem_layout_str = get_string(device, intf.iInterface)
     mem_layout = mem_layout_str.split('/')
-    addr = int(mem_layout[1], 0)
-    segments = mem_layout[2].split(',')
-    seg_re = re.compile(r'(\d+)\*(\d+)(.)(.)')
     result = []
+    for mem_layout_index in range(1, len(mem_layout), 2):
+        addr = int(mem_layout[mem_layout_index], 0)
+        segments = mem_layout[mem_layout_index + 1].split(',')
+        seg_re = re.compile(r'(\d+)\*(\d+)(.)(.)')
         for segment in segments:
             seg_match = seg_re.match(segment)
             num_pages = int(seg_match.groups()[0], 10)