[crypto] Pass image as parameter to CMS functions

[crypto] Pass image as parameter to CMS functions

The cms_signature() and cms_verify() functions currently accept raw
data pointers.  This will not be possible for cms_decrypt(), which
will need the ability to extract fragments of ASN.1 data from a
potentially large image.

Change cms_signature() and cms_verify() to accept an image as an input
parameter, and move the responsibility for setting the image trust
flag within cms_verify() since that now becomes a more natural fit.

Signed-off-by: Michael Brown <mcb30@ipxe.org>