Speed up the generation of storage format test cases

Restore the optimization done in
 HEAD^{/Speed up the generation of storage format test cases}
which was lost during refactoring made when adding support for
implicit usage flags.

There are still more than one call to the C compiler, but the extra
calls are only for some key usage test cases.

This is an internal refactoring. This commit does not change the
output of generate_psa_tests.py

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

tests/scripts/generate_psa_tests.py

@@ -495,7 +495,8 @@ class StorageFormat:
         # test cases. This allows all required information to be obtained in
         # one go, which is a significant performance gain as the information
         # includes numerical values obtained by compiling a C program.
-        for key in self.generate_all_keys():
+        all_keys = list(self.generate_all_keys())
+        for key in all_keys:
             if key.location_value() != 0:
                 # Skip keys with a non-default location, because they
                 # require a driver and we currently have no mechanism to