use CmakeLists scope to generate te XML file

- the only difference really is, that scope (the configuration.cmake) is already passed
  to px_process_params via the argument --scope. The Paths in --scope are evaluated w.r.t
  the path to src provided via the -s /--src-path argument.
- if no --scope is proveided. the Old scheme by simply walking the full --src-path directory
  is applied

Tools/px4params/srcscanner.py

@@ -1,6 +1,7 @@
 import os
 import re
 import codecs
+import sys
 
 class SourceScanner(object):
     """
@@ -8,24 +9,25 @@ class SourceScanner(object):
     to the Parser.
     """
 
-    def ScanDir(self, srcdir, parser):
+    def ScanDir(self, srcdirs, parser):
         """
         Scans provided path and passes all found contents to the parser using
         parser.Parse method.
         """
         extensions1 = tuple([".h"])
         extensions2 = tuple([".cpp", ".c"])
-        for dirname, dirnames, filenames in os.walk(srcdir):
-            for filename in filenames:
-                if filename.endswith(extensions1):
-                    path = os.path.join(dirname, filename)
-                    if not self.ScanFile(path, parser):
-                        return False
-            for filename in filenames:
-                if filename.endswith(extensions2):
-                    path = os.path.join(dirname, filename)
-                    if not self.ScanFile(path, parser):
-                        return False
+        for srcdir in srcdirs:
+            for dirname, dirnames, filenames in os.walk(srcdir):
+                for filename in filenames:
+                    if filename.endswith(extensions1):
+                        path = os.path.join(dirname, filename)
+                        if not self.ScanFile(path, parser):
+                            return False
+                for filename in filenames:
+                    if filename.endswith(extensions2):
+                        path = os.path.join(dirname, filename)
+                        if not self.ScanFile(path, parser):
+                            return False
         return True
 
     def ScanFile(self, path, parser):