arm: MVE: Fix polymorphism for scalars and constants

arm: MVE: Fix polymorphism for scalars and constants

This patch merges some polymorphic functions that were uncorrectly separating
scalar variants. It also simplifies the way we detect scalars and constants in
mve_typeid.

I also fixed some polymorphic intrinsics that were splitting of scalar cases.

gcc/ChangeLog:
2020-04-07  Andre Vieira  <andre.simoesdiasvieira@arm.com>

	* config/arm/arm_mve.h (vsubq_n): Merge with...
	(vsubq): ... this.
	(vmulq_n): Merge with...
	(vmulq): ... this.
	(__ARM_mve_typeid): Simplify scalar and constant detection.

gcc/testsuite/ChangeLog:
2020-04-07  Andre Vieira  <andre.simoesdiasvieira@arm.com>

	* gcc.target/arm/mve/intrinsics/vmulq_n_f16.c: Fix test.
	* gcc.target/arm/mve/intrinsics/vmulq_n_f32.c: Likewise.
	* gcc.target/arm/mve/intrinsics/vmulq_n_s16.c: Likewise.
	* gcc.target/arm/mve/intrinsics/vmulq_n_s32.c: Likewise.
	* gcc.target/arm/mve/intrinsics/vmulq_n_s8.c: Likewise.
	* gcc.target/arm/mve/intrinsics/vmulq_n_u16.c: Likewise.
	* gcc.target/arm/mve/intrinsics/vmulq_n_u32.c: Likewise.
	* gcc.target/arm/mve/intrinsics/vmulq_n_u8.c: Likewise.