[llvm] [M68k] always use movem for register spills (PR #106715)

[via llvm-commits]

knickish wrote:

Trying to repro this, may be spurious as this build doesn't even appear to target m68k

```
...
-- Targeting LoongArch
-- Targeting Mips
-- Targeting MSP430
-- Targeting NVPTX
...
```

https://github.com/llvm/llvm-project/pull/106715