aarch64: Use type-qualified builtins for PMUL[L] Neon intrinsics

aarch64: Use type-qualified builtins for PMUL[L] Neon intrinsics

Declare poly type-qualified builtins and use them for PMUL[L] Neon
intrinsics. This removes the need for casts in arm_neon.h.

gcc/ChangeLog:

2021-11-08  Jonathan Wright  <jonathan.wright@arm.com>

	* config/aarch64/aarch64-simd-builtins.def: Use poly type
	qualifier in builtin generator macros.
	* config/aarch64/arm_neon.h (vmul_p8): Use type-qualified
	builtin and remove casts.
	(vmulq_p8): Likewise.
	(vmull_high_p8): Likewise.
	(vmull_p8): Likewise.