The documentation doesn't say you can't call these functions more than
once on the same context, and if you do it shouldn't result in a memory
leak. Historically, the call to mbedtls_asn1_free_named_data_list() in
mbedtls_x509_string_to_names() (that was removed in the previous commit)
was ensuring that. Let's restore it where it makes sense. (These are the
only 3 places calling mbedtls_x509_string_to_names() in the library.)
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>