evm: Rename is_unsupported_fs to is_unsupported_hmac_fs

Rename is_unsupported_fs to is_unsupported_hmac_fs since now only HMAC is
unsupported.

Co-developed-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>