Split test generator base class

The class BaseTarget served two purposes:
- track test cases and target files for generation
- provide an abstract base class for individual test groups

Splitting these allows decoupling these two and to have further common
superclasses across targets.

No intended change in generated test cases.

Signed-off-by: Janos Follath <janos.follath@arm.com>

scripts/mbedtls_dev/bignum_common.py

@@ -17,6 +17,8 @@
 from abc import abstractmethod
 from typing import Iterator, List, Tuple, TypeVar
 
+from . import test_data_generation
+
 T = TypeVar('T') #pylint: disable=invalid-name
 
 def invmod(a: int, n: int) -> int:
@@ -63,8 +65,7 @@ def combination_pairs(values: List[T]) -> List[Tuple[T, T]]:
     """Return all pair combinations from input values."""
     return [(x, y) for x in values for y in values]
 
-
-class OperationCommon:
+class OperationCommon(test_data_generation.BaseTest):
     """Common features for bignum binary operations.
 
     This adds functionality common in binary operation tests.