[llvm] [GlobalIsel][AArch64] legalize ptr add (PR #89218)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

Test:
```
define <4 x ptr> @ptr_add_4_vector_ptr(ptr %vec, <4 x i32> %offset) {
  %ptr_add = getelementptr i8, ptr %vec, <4 x i32> %offset
  ret <4 x ptr> %ptr_add
}
```

https://github.com/llvm/llvm-project/pull/89218