[TableGen][GlobalISel] Have the predicate directly know which data they are dealing with

Prior to this patch, a predicate wouldn't make sense outside of its
rule. Indeed, it was only during emitting a rule that a predicate would
be made aware of the IDs of the data it is checking. Because of that,
predicates could not be moved around or compared between each other.

NFC.

llvm-svn: 320887