[vect] Outline code into new function: determine_peel_for_niter

gcc/ChangeLog:
2019-10-17  Andre Vieira  <andre.simoesdiasvieira@arm.com>

	* tree-vect-loop.c (determine_peel_for_niter): New function contained
	outlined code from ...
	(vect_analyze_loop_2): ... here.

From-SVN: r277103