i386: Use CONST_VECTOR_P predicate instead of open coding it

i386: Use CONST_VECTOR_P predicate instead of open coding it

No functional changes.

gcc/ChangeLog:

	* config/i386/i386-expand.cc (ix86_expand_vector_logical_operator):
	Use CONST_VECTOR_P instead of open coding it.
	(ix86_expand_int_sse_cmp): Ditto.
	(ix86_extract_perm_from_pool_constant): Ditto.
	(ix86_split_to_parts): Ditto.
	(const_vector_equal_evenodd_p): Ditto.
	* config/i386/i386.cc (ix86_print_operand): Ditto.
	* config/i386/predicates.md (zero_extended_scalar_load_operand): Ditto.
	(float_vector_all_ones_operand): Ditto.
	* config/i386/sse.md (avx512vl_vextractf128<mode>): Ditto.