arm: ACLE intrinsics for bfloat16 dot product

arm: ACLE intrinsics for bfloat16 dot product

This patch is part of a series adding support for Armv8.6-A features.
It adds intrinsics for brain half-precision float-point (BF16) dot
instructions with AdvSIMD support.

gcc/ChangeLog:

2020-02-25  Dennis Zhang  <dennis.zhang@arm.com>

	* config/arm/arm_neon.h (vbfdot_f32, vbfdotq_f32): New
	(vbfdot_lane_f32, vbfdotq_laneq_f32): New.
	(vbfdot_laneq_f32, vbfdotq_lane_f32): New.
	* config/arm/arm_neon_builtins.def (vbfdot): New entry.
	(vbfdot_lanev4bf, vbfdot_lanev8bf): Likewise.
	* config/arm/iterators.md (VSF2BF): New attribute.
	* config/arm/neon.md (neon_vbfdot<VCVTF:mode>): New entry.
	(neon_vbfdot_lanev4bf<VCVTF:mode>): Likewise.
	(neon_vbfdot_lanev8bf<VCVTF:mode>): Likewise.

gcc/testsuite/ChangeLog:

2020-02-25  Dennis Zhang  <dennis.zhang@arm.com>

	* gcc.target/arm/simd/bf16_dot_1.c: New test.
	* gcc.target/arm/simd/bf16_dot_2.c: New test.
	* gcc.target/arm/simd/bf16_dot_3.c: New test.