Bignum test: Move identical function to superclass

No intended change in generated test cases.

Signed-off-by: Janos Follath <janos.follath@arm.com>
diff --git a/scripts/mbedtls_dev/bignum_common.py b/scripts/mbedtls_dev/bignum_common.py
index ba30be4..0224114 100644
--- a/scripts/mbedtls_dev/bignum_common.py
+++ b/scripts/mbedtls_dev/bignum_common.py
@@ -17,6 +17,7 @@
 from abc import abstractmethod
 from typing import Iterator, List, Tuple, TypeVar
 
+from . import test_case
 from . import test_data_generation
 
 T = TypeVar('T') #pylint: disable=invalid-name
@@ -122,6 +123,11 @@
             )
         yield from cls.input_cases
 
+    @classmethod
+    def generate_function_tests(cls) -> Iterator[test_case.TestCase]:
+        for a_value, b_value in cls.get_value_pairs():
+            yield cls(a_value, b_value).create_test_case()
+
 # BEGIN MERGE SLOT 1
 
 # END MERGE SLOT 1