[ipgen] Explicitly load config files as UTF-8

We explicitly save configuration files as UTF-8, ensure we load them the
same way.

Signed-off-by: Philipp Wagner <phw@lowrisc.org>
diff --git a/util/ipgen/lib.py b/util/ipgen/lib.py
index e1453e7..c90198d 100644
--- a/util/ipgen/lib.py
+++ b/util/ipgen/lib.py
@@ -189,7 +189,8 @@
     @classmethod
     def from_text(cls, txt: str, where: str) -> 'IpConfig':
         """Load an IpConfig from an Hjson description in txt"""
-        return cls.from_raw(hjson.loads(txt, use_decimal=True), where)
+        return cls.from_raw(
+            hjson.loads(txt, use_decimal=True, encoding="UTF-8"), where)
 
     def to_file(self, file_path: Path, header: Optional[str] = ""):
         obj = {}