`(vect128 int){1, 1, 0, 0}` could be generated via `movi vN.2s, 1`

From my GCC bug report: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113926

```c
#define vect128 __attribute__((vector_size(16) ))
vect128 int f1(void)
{
return (vect128 int){1, 1, 0, 0};
}
```

This should just produce `movi v0.2s, 1`.