[build] Implement registers code generation in the Rust meta crate;

lib/codegen/meta-python/cdsl/registers.py

@@ -87,7 +87,6 @@ class RegBank(object):
         self.names = names
         self.classes = list()  # type: List[RegClass]
         self.toprcs = list()  # type: List[RegClass]
-        self.first_toprc_index = None  # type: int
 
         assert len(names) <= units
 
@@ -248,7 +247,7 @@ class RegClass(object):
     def intersect(self, other):
         # type: (RegClass) -> RCTup
         """
-        Get a tuple representing the intersction of two register classes.
+        Get a tuple representing the intersection of two register classes.
 
         Returns `None` if the two classes are disjoint.
         """