arm: MVE Fix immediate constraints on some vector instructions

arm: MVE Fix immediate constraints on some vector instructions

Hi,

This patch fixes the immediate checks on vcvt and vqshr(u)n[bt] instructions.
It also removes the 'arm_mve_immediate_check' as the check was wrong and the
error message is not much better than the constraint one, which albeit isn't
great either.

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

	* config/arm/arm.c (arm_mve_immediate_check): Removed.
	* config/arm/mve.md (MVE_pred2, MVE_constraint2): Added FP types.
	(mve_vcvtq_n_to_f_*, mve_vcvtq_n_from_f_*, mve_vqshrnbq_n_*,
	 mve_vqshrntq_n_*, mve_vqshrunbq_n_s*, mve_vqshruntq_n_s*,
	 mve_vcvtq_m_n_from_f_*, mve_vcvtq_m_n_to_f_*, mve_vqshrnbq_m_n_*,
	 mve_vqrshruntq_m_n_s*, mve_vqshrunbq_m_n_s*,
	 mve_vqshruntq_m_n_s*): Fixed immediate constraints.

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

	* gcc.target/arm/mve/intrinsics/mve_immediates_1_n.c: New test.