aarch64: Use RTL builtins for vpadal_[su]32 intrinsics

aarch64: Use RTL builtins for vpadal_[su]32 intrinsics

Rewrite vpadal_[su]32 Neon intrinsics to use RTL builtins rather than
inline assembly code, allowing for better scheduling and
optimization.

gcc/ChangeLog:

2021-02-09  Jonathan Wright  <jonathan.wright@arm.com>

	* config/aarch64/aarch64-simd-builtins.def: Use VDQV_L
	iterator to generate [su]adalp RTL builtins.
	* config/aarch64/aarch64-simd.md: Use VDQV_L iterator in
	[su]adalp RTL pattern.
	* config/aarch64/arm_neon.h (vpadal_s32): Use RTL builtin
	instead of inline asm.
	(vpadal_u32): Likewise.