aarch64: Revert bogus fix for PR105254

aarch64: Revert bogus fix for PR105254

In f2ebf2d98efe0ac2314b58cf474f44cb8ebd5244 I'd forced the
chosen unroll factor to be a factor of the VF, in order to
work around an exact_div ICE in PR105254.  This was completely
bogus -- clearly I didn't look in enough detail at why we ended
up with an unrolled VF that wasn't a multiple of the UF.

Kewen has since fixed the bug properly for PR105940, so this
patch reverts my earlier attempt.  Sorry for the stupidity.

gcc/
	PR tree-optimization/105254
	PR tree-optimization/105940

	Revert:

	* config/aarch64/aarch64.cc
	(aarch64_vector_costs::determine_suggested_unroll_factor): Take a
	loop_vec_info as argument.  Restrict the unroll factor to values
	that divide the VF.
	(aarch64_vector_costs::finish_cost): Update call accordingly.

gcc/testsuite/
	* gcc.target/aarch64/sve/cost_model_14.c: New test.