Set the key size as an attribute

Instead of passing a separate parameter for the key size to
psa_generate_key and psa_generator_import_key, set it through the
attributes, like the key type and other metadata.
diff --git a/tests/suites/test_suite_psa_crypto.data b/tests/suites/test_suite_psa_crypto.data
index 5b99b84..c91094c 100644
--- a/tests/suites/test_suite_psa_crypto.data
+++ b/tests/suites/test_suite_psa_crypto.data
@@ -2,7 +2,7 @@
 static_checks:
 
 PSA key attributes structure
-attributes_set_get:0x6963:PSA_KEY_LIFETIME_PERSISTENT:PSA_KEY_USAGE_ENCRYPT | PSA_KEY_USAGE_DECRYPT:PSA_ALG_CCM:PSA_KEY_TYPE_AES
+attributes_set_get:0x6963:PSA_KEY_LIFETIME_PERSISTENT:PSA_KEY_USAGE_ENCRYPT | PSA_KEY_USAGE_DECRYPT:PSA_ALG_CCM:PSA_KEY_TYPE_AES:128
 
 PSA import/export raw: 0 bytes
 import_export:"":PSA_KEY_TYPE_RAW_DATA:0:PSA_KEY_USAGE_EXPORT:0:0:PSA_SUCCESS:1