efisiglist: convert the hex array properly

Signed-off-by: Gary Ching-Pang Lin <glin@suse.com>
efisiglist: Correct the calulation of SignatureListSize

Signed-off-by: Gary Ching-Pang Lin <glin@suse.com>
efisiglist: support adding a certificate in DER form

Signed-off-by: Gary Ching-Pang Lin <glin@suse.com>