aarch64: Use type-qualified builtins for ADDP Neon intrinsics

aarch64: Use type-qualified builtins for ADDP Neon intrinsics

Declare unsigned type-qualified builtins and use them to implement
the pairwise addition Neon intrinsics. This removes the need for many
casts in arm_neon.h.

gcc/ChangeLog:

2021-11-09  Jonathan Wright  <jonathan.wright@arm.com>

	* config/aarch64/aarch64-simd-builtins.def:
	* config/aarch64/arm_neon.h (vpaddq_u8): Use type-qualified
	builtin and remove casts.
	(vpaddq_u16): Likewise.
	(vpaddq_u32): Likewise.
	(vpaddq_u64): Likewise.
	(vpadd_u8): Likewise.
	(vpadd_u16): Likewise.
	(vpadd_u32): Likewise.
	(vpaddd_u64): Likewise.