Bignum tests: flatten class hierarchy in _core

There is no semantic changes to the generated tests, the order of the
test blocks has changed.

Signed-off-by: Janos Follath <janos.follath@arm.com>
diff --git a/scripts/mbedtls_dev/bignum_core.py b/scripts/mbedtls_dev/bignum_core.py
index deff6a8..806e131 100644
--- a/scripts/mbedtls_dev/bignum_core.py
+++ b/scripts/mbedtls_dev/bignum_core.py
@@ -107,12 +107,7 @@
                        .create_test_case())
 
 
-class BignumCoreOperation(BignumCoreTarget, bignum_common.OperationCommon):
-    #pylint: disable=abstract-method
-    """Common features for bignum core operations."""
-
-
-class BignumCoreAddAndAddIf(BignumCoreOperation):
+class BignumCoreAddAndAddIf(BignumCoreTarget, bignum_common.OperationCommon):
     """Test cases for bignum core add and add-if."""
     count = 0
     symbol = "+"
@@ -131,7 +126,7 @@
         ]
 
 
-class BignumCoreSub(BignumCoreOperation):
+class BignumCoreSub(BignumCoreTarget, bignum_common.OperationCommon):
     """Test cases for bignum core sub."""
     count = 0
     symbol = "-"
@@ -157,7 +152,7 @@
         ]
 
 
-class BignumCoreMLA(BignumCoreOperation):
+class BignumCoreMLA(BignumCoreTarget, bignum_common.OperationCommon):
     """Test cases for fixed-size multiply accumulate."""
     count = 0
     test_function = "mpi_core_mla"