AVX512FP16: Add reduce operators(add/mul/min/max).

AVX512FP16: Add reduce operators(add/mul/min/max).

gcc/ChangeLog:

	* config/i386/avx512fp16intrin.h (_MM512_REDUCE_OP): New macro
	(_mm512_reduce_add_ph): New intrinsic.
	(_mm512_reduce_mul_ph): Ditto.
	(_mm512_reduce_min_ph): Ditto.
	(_mm512_reduce_max_ph): Ditto.
	* config/i386/avx512fp16vlintrin.h
	(_MM256_REDUCE_OP/_MM_REDUCE_OP): New macro.
	(_mm256_reduce_add_ph): New intrinsic.
	(_mm256_reduce_mul_ph): Ditto.
	(_mm256_reduce_min_ph): Ditto.
	(_mm256_reduce_max_ph): Ditto.
	(_mm_reduce_add_ph): Ditto.
	(_mm_reduce_mul_ph): Ditto.
	(_mm_reduce_min_ph): Ditto.
	(_mm_reduce_max_ph): Ditto.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/avx512fp16-reduce-op-1.c: New test.
	* gcc.target/i386/avx512fp16vl-reduce-op-1.c: Ditto.