[mlir][sve][nfc] Merge the integration tests for linalg.matmul (#74059)

At the moment the logic to tile and vectorize `linalg.matmul` is
duplicated in multiple test files:
  * matmul.mlir
  * matmul_mixed_ty.mlir

Instead, this patch uses `transform.foreach` to apply the same sequence
to multiple functions within the same test file (e.g. `matmul_f32` and
`matmul_mixed_ty` as defined in the original files). This allows us to
merge relevant test files.