aarch64: Use RTL builtins for vpaddq intrinsics

aarch64: Use RTL builtins for vpaddq intrinsics

Rewrite vpaddq Neon intrinsics to use RTL builtins rather than inline
assembly code, allowing for better scheduling and optimization.

gcc/ChangeLog:

2021-02-08  Jonathan Wright  <jonathan.wright@arm.com>

	* config/aarch64/aarch64-simd-builtins.def: Use VDQ_I iterator
	for aarch64_addp<mode> builtin macro generator.
	* config/aarch64/aarch64-simd.md: Use VDQ_I iterator in
	aarch64_addp<mode> RTL pattern.
	* config/aarch64/arm_neon.h (vpaddq_s8): Use RTL builtin
	instead of inline asm.
	(vpaddq_s16): Likewise.
	(vpaddq_s32): Likewise.
	(vpaddq_s64): Likewise.
	(vpaddq_u8): Likewise.
	(vpaddq_u16): Likewise.
	(vpaddq_u32): Likewise.
	(vpaddq_u64): Likewise.