arm: Auto-vectorization for MVE: vmin/vmax

arm: Auto-vectorization for MVE: vmin/vmax

This patch enables MVE vmin/vmax instructions for auto-vectorization.
MVE target is included in expander smin<mode>3, umin<mode>3, smax<mode>3
and umax<mode>3 for vectorization. Related insns for vmin/vmax in mve.md
are modified to use smin, umin, smax and umax expressions instead of
unspec to support the expanders.

gcc/ChangeLog:

2020-10-22  Dennis Zhang  <dennis.zhang@arm.com>

	* config/arm/mve.md (mve_vmaxq_<supf><mode>): Replace with ...
	(mve_vmaxq_s<mode>, mve_vmaxq_u<mode>): ... these new insns to
	use smax/umax instead of VMAXQ.
	(mve_vminq_<supf><mode>): Replace with ...
	(mve_vminq_s<mode>, mve_vminq_u<mode>): ... these new insns to
	use smin/umin instead of VMINQ.
	(mve_vmaxnmq_f<mode>): Use smax instead of VMAXNMQ_F.
	(mve_vminnmq_f<mode>): Use smin instead of VMINNMQ_F.
	* config/arm/vec-common.md (smin<mode>3): Use the new mode macros
	ARM_HAVE_<MODE>_ARITH.
	(umin<mode>3, smax<mode>3, umax<mode>3): Likewise.

gcc/testsuite/ChangeLog:

	* gcc.target/arm/simd/mve-vminmax_1.c: New test.