Move some arm_neon.h functions which currently use assembly over
to intrinsics.

2020-02-18  James Greenhalgh  <james.greenhalgh@arm.com>

gcc/
	* config/aarch64/aarch64-simd-builtins.def
	(intrinsic_vec_smult_lo_): New.
	(intrinsic_vec_umult_lo_): Likewise.
	(vec_widen_smult_hi_): Likewise.
	(vec_widen_umult_hi_): Likewise.
	* config/aarch64/aarch64-simd.md
	(aarch64_intrinsic_vec_<su>mult_lo_<mode>): New.
	* config/aarch64/arm_neon.h (vmull_high_s8): Use intrinsics.
	(vmull_high_s16): Likewise.
	(vmull_high_s32): Likewise.
	(vmull_high_u8): Likewise.
	(vmull_high_u16): Likewise.
	(vmull_high_u32): Likewise.
	(vmull_s8): Likewise.
	(vmull_s16): Likewise.
	(vmull_s32): Likewise.
	(vmull_u8): Likewise.
	(vmull_u16): Likewise.
	(vmull_u32): Likewise.

gcc/testsuite/
	* gcc.target/aarch64/vmull_high.c: New.