This patch adds the ARMv8.6 ACLE intrinsics for vmmla, vfmab and vfmat 
as part of the BFloat16 extension.
(https://developer.arm.com/docs/101028/latest.)
The intrinsics are declared in arm_neon.h and the RTL patterns are 
defined in neon.md.
Two new tests are added to check assembler output and lane indices.

This patch depends on the Arm back-end patche. 
(https://gcc.gnu.org/ml/gcc-patches/2019-12/msg01448.html)

Tested for regression on arm-none-eabi and armeb-none-eabi. I don't have 
commit rights, so if this is ok can someone please commit it for me?

gcc/ChangeLog:

2019-11-12  Delia Burduv  <delia.burduv@arm.com>

	* config/arm/arm_neon.h (vbfmmlaq_f32): New.
	  (vbfmlalbq_f32): New.
	  (vbfmlaltq_f32): New.
	  (vbfmlalbq_lane_f32): New.
	  (vbfmlaltq_lane_f32): New.
   	  (vbfmlalbq_laneq_f32): New.
	  (vbfmlaltq_laneq_f32): New.
	* config/arm/arm_neon_builtins.def (vbfmmla): New.
           (vbfmab): New.
           (vbfmat): New.
           (vbfmab_lane): New.
           (vbfmat_lane): New.
           (vbfmab_laneq): New.
           (vbfmat_laneq): New.
  	* config/arm/iterators.md (BF_MA): New int iterator.
           (bt): New int attribute.
           (VQXBF): Copy of VQX with V8BF.
           (V_HALF): Added V8BF.
   	* config/arm/neon.md (neon_vbfmmlav8hi): New insn.
           (neon_vbfma<bt>v8hi): New insn.
           (neon_vbfma<bt>_lanev8hi): New insn.
           (neon_vbfma<bt>_laneqv8hi): New expand.
           (neon_vget_high<mode>): Changed iterator to VQXBF.
	* config/arm/unspecs.md (UNSPEC_BFMMLA): New UNSPEC.
           (UNSPEC_BFMAB): New UNSPEC.
           (UNSPEC_BFMAT): New UNSPEC.

2019-11-12  Delia Burduv  <delia.burduv@arm.com>

         * gcc.target/arm/simd/bf16_ma_1.c: New test.
         * gcc.target/arm/simd/bf16_ma_2.c: New test.
         * gcc.target/arm/simd/bf16_mmla_1.c: New test.