[TableGen] Handle RegClassByHwMode in AsmWriter
Previously, we were emitting a broken AliasPatternCond array, outputting
`MyTarget::RegClassByHwModeRegClassID` which does not exist.
Instead, we now add a new predicate and pass the RegClassByHwMode index
as the value argument.
Pull Request: https://github.com/llvm/llvm-project/pull/171264
