[mlir][spirv] Use symbolize functions in enum attribute predicates

By default, for an enum attribute, we will generate a list of equality
comparisons for all supported cases inside it's predicate. This list
can be fairly large for certain SPIR-V enum attributes. Instead, we
already have such a list generated by EnumsGen in the symbolize
functions. Leverage that to simplify the generated C++ code.

Differential Revision: https://reviews.llvm.org/D72763