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/scope.py

@@ -0,0 +1,32 @@
+import os
+import re
+
+class Scope(object):
+    """
+    Single parameter group
+    """
+    re_deep_lines = re.compile(r'.*\/.*\/')
+    def __init__(self,):
+        self.scope = set()
+
+
+    def __str__(self):
+        return self.scope.__str__()
+
+    def Add(self, scope):
+        """
+        Add Scope to set
+        """
+        self.scope.add(scope)
+
+    def Has(self, scope):
+        """
+        Check for existance
+        """
+        if len(self.scope) == 0:
+            return True
+        # Anything in the form xxxxx/yyyyy/zzzzz....
+        # is treated as xxxxx/yyyyy
+        while (self.re_deep_lines.match(scope)):
+            scope = os.path.dirname(scope)
+        return scope in self.scope