[LoongArch] Explicitly specify instruction properties

This revision explicitly specifies the machine instruction properties instead of relying on guesswork. This is because guessing instruction properties has proven to be inaccurate, such as the machine LICM not working:

```
void func(char *a, char *b)
{
    int i;

    for (i = 0; i != 72526; i++)
        a[i] = b[i];
}
```

Guessing instruction properties:

```
func:                                   # @func
        move    $a2, $zero
.LBB0_1:                                # =>This Inner Loop Header: Depth=1
        ldx.b   $a3, $a1, $a2
        stx.b   $a3, $a0, $a2
        addi.d  $a2, $a2, 1
        lu12i.w $a3, 17
        ori     $a3, $a3, 2894
        bne     $a2, $a3, .LBB0_1
        ret
.Lfunc_end0:
```

Explicitly specify instruction properties:

```
func:                                   # @func
        lu12i.w $a2, 17
        ori     $a2, $a2, 2894
        move    $a3, $zero
.LBB0_1:                                # =>This Inner Loop Header: Depth=1
        ldx.b   $a4, $a1, $a3
        stx.b   $a4, $a0, $a3
        addi.d  $a3, $a3, 1
        bne     $a3, $a2, .LBB0_1
        ret
.Lfunc_end0:
```

Reviewed By: SixWeining, xen0n

Differential Revision: https://reviews.llvm.org/D154192