aarch64: Reimplement vget_high* intrinsics

aarch64: Reimplement vget_high* intrinsics

Similar to the vget_low* intrinsics we should just use a proper vec_select rather than
going through V2DI subregs.

gcc/ChangeLog:

	* config/aarch64/aarch64-simd-builtins.def (get_high): Define builtin.
	* config/aarch64/aarch64-simd.md (aarch64_get_high<mode>): Define.
	* config/aarch64/arm_neon.h (__GET_HIGH): Delete.
	(vget_high_f16): Reimplement using new builtin.
	(vget_high_f32): Likewise.
	(vget_high_f64): Likewise.
	(vget_high_p8): Likewise.
	(vget_high_p16): Likewise.
	(vget_high_p64): Likewise.
	(vget_high_s8): Likewise.
	(vget_high_s16): Likewise.
	(vget_high_s32): Likewise.
	(vget_high_s64): Likewise.
	(vget_high_u8): Likewise.
	(vget_high_u16): Likewise.
	(vget_high_u32): Likewise.
	(vget_high_u64): Likewise.