scsi: target: iscsi: CHAP: add support for SHA1, SHA256 and SHA3-256

scsi: target: iscsi: CHAP: add support for SHA1, SHA256 and SHA3-256

This patch modifies the chap_server_compute_hash() function to make it
agnostic to the choice of hash algorithm that is used.  It also adds
support to three new hash algorithms: SHA1, SHA256 and SHA3-256.

The chap_got_response() function has been removed because the digest type
validity is already checked by chap_server_open()

Link: https://lore.kernel.org/r/20191028123822.5864-2-mlombard@redhat.com
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Tested-by: Chris Leech <cleech@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>