arm: vst1q_types_x2 ACLE intrinsics

arm: vst1q_types_x2 ACLE intrinsics

This patch is part of a series of patches implementing the _xN
variants of the vst1q intrinsic for the arm port. This patch adds the
_x2 variants of the vst1q intrinsic.

ACLE documents:
https://developer.arm.com/documentation/ihi0053/latest/

ISA documents:
https://developer.arm.com/documentation/ddi0487/latest/

gcc/ChangeLog:
	* config/arm/arm_neon.h
	(vst1q_u8_x2, vst1q_u16_x2, vst1q_u32_x2, vst1q_u64_x2): New.
	(vst1q_s8_x2, vst1q_s16_x2, vst1q_s32_x2, vst1q_s64_x2): New.
	(vst1q_f16_x2, vst1q_f32_x2): New.
	(vst1q_p8_x2, vst1q_p16_x2, vst1q_p64_x2): New.
	(vst1q_bf16_x2): New.
	* config/arm/arm_neon_builtins.def (vst1q_x2): New entries.
	* config/arm/neon.md
	(neon_vst1<VMEMX2_q>_x2<VDQX:mode>): Updated from
	neon_vst1_x2<mode>.
	* config/arm/iterators.md (VMEMX2): New mode iterator.
	(VMEMX2_q): New mode attribute.

gcc/testsuite/ChangeLog:
	* gcc.target/arm/simd/vst1q_base_xN_1.c: Add new tests.
	* gcc.target/arm/simd/vst1q_bf16_xN_1.c: Add new tests.
	* gcc.target/arm/simd/vst1q_fp16_xN_1.c: Add new tests.
	* gcc.target/arm/simd/vst1q_p64_xN_1.c: Add new tests.