[llvm] [mlir] [TableGen] Add assert to validate `Objects` list for `HwModeSelect` (PR #123794)

[Rahul Joshi via llvm-commits]

jurahul wrote:

@topperc and @s-barannikov PTAL. I also considered splitting it into 2 changes: one for the TableGen main behavior and the HwModeSelect assert as a second one. If the overall change seems ok, I can do that

https://github.com/llvm/llvm-project/pull/123794