aarch64: Use type-qualified builtins for vcombine_* Neon intrinsics

aarch64: Use type-qualified builtins for vcombine_* Neon intrinsics

Declare unsigned and polynomial type-qualified builtins for
vcombine_* Neon intrinsics. Using these builtins removes the need for
many casts in arm_neon.h.

gcc/ChangeLog:

2021-11-10  Jonathan Wright  <jonathan.wright@arm.com>

	* config/aarch64/aarch64-builtins.c (TYPES_COMBINE): Delete.
	(TYPES_COMBINEP): Delete.
	* config/aarch64/aarch64-simd-builtins.def: Declare type-
	qualified builtins for vcombine_* intrinsics.
	* config/aarch64/arm_neon.h (vcombine_s8): Remove unnecessary
	cast.
	(vcombine_s16): Likewise.
	(vcombine_s32): Likewise.
	(vcombine_f32): Likewise.
	(vcombine_u8): Use type-qualified builtin and remove casts.
	(vcombine_u16): Likewise.
	(vcombine_u32): Likewise.
	(vcombine_u64): Likewise.
	(vcombine_p8): Likewise.
	(vcombine_p16): Likewise.
	(vcombine_p64): Likewise.
	(vcombine_bf16): Remove unnecessary cast.
	* config/aarch64/iterators.md (VD_I): New mode iterator.
	(VDC_P): New mode iterator.