Switch from cElementTree to ElementTree.

The xml.etree.cElementTree module will be removed in Python 3.9. Since
Python 3.3 the xml.etree.cElementTree module has been deprecated, the
xml.etree.ElementTree module uses a fast implementation whenever
available.

Builds using Python 2.7 can still work but with the slower
implementation.

Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Acked-by: Eric Engestrom <eric@engestrom.ch>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5349>

src/vulkan/util/gen_enum_to_str.py

@@ -25,7 +25,7 @@ from __future__ import print_function
 import argparse
 import os
 import textwrap
-import xml.etree.cElementTree as et
+import xml.etree.ElementTree as et
 
 from mako.template import Template
 

src/vulkan/util/vk_extensions.py

@@ -1,7 +1,7 @@
 import argparse
 import copy
 import re
-import xml.etree.cElementTree as et
+import xml.etree.ElementTree as et
 
 def _bool_to_c_expr(b):
     if b is True:

src/vulkan/util/vk_extensions_gen.py

@@ -24,7 +24,7 @@ COPYRIGHT = """\
  */
 """
 
-import xml.etree.cElementTree as et
+import xml.etree.ElementTree as et
 
 from mako.template import Template