Add generator functions to support TFL gelu

Change-Id: I1056f4a3abe9079381fb2c7d02edf11312aba9d6
Signed-off-by: TatWai Chong <tatwai.chong@arm.com>
diff --git a/verif/frameworks/test_builder.py b/verif/frameworks/test_builder.py
index 8677559..84e4d46 100644
--- a/verif/frameworks/test_builder.py
+++ b/verif/frameworks/test_builder.py
@@ -101,6 +101,13 @@
         def eval(self, a):
             return tf.nn.leaky_relu(a, alpha=self.alpha, name=self.result_name)
 
+    class Gelu:
+        def __init__(self, name):
+            self.result_name = name
+
+        def eval(self, a):
+            return tf.nn.gelu(a, name=self.result_name)
+
     class Concat:
         def __init__(self, axis, name):
             self.axis = axis