[util, topgen] Add helper functions to c.py

These are helpful for the ROM_EXT manifest header generation,
but could also be useful in future for other use-cases.

Signed-off-by: Silvestrs Timofejevs <silvestrst@lowrisc.org>
diff --git a/util/topgen/c.py b/util/topgen/c.py
index d98e16d..0884176 100644
--- a/util/topgen/c.py
+++ b/util/topgen/c.py
@@ -8,6 +8,8 @@
 
 from mako.template import Template
 
+from math import ceil
+
 
 class Name(object):
     """We often need to format names in specific ways; this class does so."""
@@ -52,13 +54,20 @@
         self.name = name
         self.base_addr = base_addr
         self.size_bytes = size_bytes
+        self.size_words = ceil(int(str(size_bytes), 0) / 4)
 
     def base_addr_name(self):
         return self.name + Name(["base", "addr"])
 
+    def offset_name(self):
+        return self.name + Name(["offset"])
+
     def size_bytes_name(self):
         return self.name + Name(["size", "bytes"])
 
+    def size_words_name(self):
+        return self.name + Name(["size", "words"])
+
 
 class CEnum(object):
     def __init__(self, name):