Express enumerations that are not defined in the current XSD but per nomartive text explictitly via cddl rules

[henkbirkholz]

There still might be a few cases left, where the value is text, but semantically it is a type-choice / enumeration. This should be double checked before meeting 102.

[henkbirkholz]

Used role (label 33) & rel (label 40) as proposal by example. The roles & rels type-choices still require an extension-point, I assume.

media (label 10) is currently a text value with a semantic that is a tad bit more complex than a type-choice: "EXPRESSION [[OPERATOR] [EXPRESSION] ... ]", where EXPRESSION can be a simple type-choice.... or ... "([PREFIX-]ENVIRONMENT.ATTRIBUTE:VALUE)" ... and so on and on....

I propose to deal with.... that in cddl, too.

Also, the definition of rel seems to be wrong at the moment, as every SWID enumeration is actually NOT defined in https://www.iana.org/assignments/link-relations/link-relations.xhtml

This needs fixing.

[henkbirkholz]

Addressed (with the exception of #6).
Leaving this open to be closed at SACM WG session in BKK.