patman: Use unicode for file I/O

At present patman test fail in some environments which don't use utf-8
as the default file encoding. Add this explicitly.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/settings.py b/tools/patman/settings.py
index c98911d..5dc83a8 100644
--- a/tools/patman/settings.py
+++ b/tools/patman/settings.py
@@ -165,7 +165,7 @@
         fname: Filename to read
     """
     try:
-        fd = open(fname, 'r')
+        fd = open(fname, 'r', encoding='utf-8')
     except IOError:
         print("Warning: Cannot find alias file '%s'" % fname)
         return
@@ -259,7 +259,7 @@
     """
     if os.path.exists(fname):
         bad_line = None
-        with open(fname) as fd:
+        with open(fname, encoding='utf-8') as fd:
             linenum = 0
             for line in fd:
                 linenum += 1