Generalize overriding llvm func attr flags in translation info

[Groverkss]

Previously, we were specifically querying for waves_per_eu attr in translation info in ROCMTarget. This patch makes this general by attaching a llvm function attribute override dictionary in the translation info instead which can be set.

[Groverkss]

Not sure where to add tests for checking if serialization works

[qedawkins]

Not sure where to add tests for checking if serialization works

Yeah good question. I wonder if there is an llvm attribute that would do something we could lit test against.

[MaheshRavishankar]

Not sure where to add tests for checking if serialization works

I am not sure there is an easy way. You probably need to dump the IR after the OPT phase, but before LLC phase and check the flag exists..