[llvm] [GISel][TableGen] Generate getRegBankFromRegClass (PR #99896)

[Kai Nacke via llvm-commits]

redstar wrote:

I know that test cases are missing. I'll add them when it becomes clear that this is the way to go.

On Power, building targets all + m68k, this change adds 1472 bytes to llc.

Possible alternative approaches which I have not examined:
- compact the table further (increases access time)
- generate a large switch
- generate a perfect hash function (may not save much space)

https://github.com/llvm/llvm-project/pull/99896