Add support for vector permute cost since various permutes can expand

Add support for vector permute cost since various permutes can expand
into a complex sequence of instructions.  This fixes major performance
regressions due to recent changes in SLP vectorizer (which now vectorizes
more aggressively and emits many complex permutes).  Set the cost to > 1
for all microarchitectures so that the number of permutes is usually zero
and regressions disappear.

2016-01-28  Wilco Dijkstra  <wdijkstr@arm.com>

	* config/aarch64/aarch64.c (generic_vector_cost):
	Set vec_permute_cost.
	(cortexa57_vector_cost): Likewise.
	(exynosm1_vector_cost): Likewise.
	(xgene1_vector_cost): Likewise.
	(aarch64_builtin_vectorization_cost): Use vec_permute_cost.
	* config/aarch64/aarch64-protos.h (cpu_vector_cost):
	Add vec_permute_cost entry.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@232922 138bc75d-0d04-0410-961f-82ee72b054a4