ivopts: Change constant_multiple_of to expand aff nodes.

ivopts: Change constant_multiple_of to expand aff nodes.

This changes the calls to tree_to_aff_combination in constant_multiple_of to
tree_to_aff_combination_expand along with associated plumbing of ivopts_data
and required cache.

This improves cases such as:

```c
void f(int *p1, int *p2, unsigned long step, unsigned long end, svbool_t pg) {
    for (unsigned long i = 0; i < end; i += step) {
        svst1(pg, p1, svld1_s32(pg, p2));
        p1 += step;
        p2 += step;
    }
}
```

Where ivopts previously didn't expand the SSA variables for the step increements
and so lacked the ability to group all the IV's and ended up with:

```
f:
	cbz	x3, .L1
	mov	x4, 0
.L3:
	ld1w	z31.s, p0/z, [x1]
	add	x4, x4, x2
	st1w	z31.s, p0, [x0]
	add	x1, x1, x2, lsl 2
	add	x0, x0, x2, lsl 2
	cmp	x3, x4
	bhi	.L3
.L1:
	ret
```

After this change we end up with:

```
f:
	cbz	x3, .L1
	mov	x4, 0
.L3:
	ld1w	z31.s, p0/z, [x1, x4, lsl 2]
	st1w	z31.s, p0, [x0, x4, lsl 2]
	add	x4, x4, x2
	cmp	x3, x4
	bhi	.L3
.L1:
	ret
```

gcc/ChangeLog:

	* tree-ssa-loop-ivopts.cc (constant_multiple_of): Change
	tree_to_aff_combination to tree_to_aff_combination_expand and add
	parameter to take ivopts_data.
	(get_computation_aff_1): Change parameters and calls to include
	ivopts_data.
	(get_computation_aff): Ditto.
	(get_computation_at) Ditto.:
	(get_debug_computation_at) Ditto.:
	(get_computation_cost) Ditto.:
	(rewrite_use_nonlinear_expr) Ditto.:
	(rewrite_use_address) Ditto.:
	(rewrite_use_compare) Ditto.:
	(remove_unused_ivs) Ditto.:

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/sve/adr_7.c: New test.