RISC-V: Add vnsrl/vnsra/vncvt/vmerge/vmv C/C++ support

RISC-V: Add vnsrl/vnsra/vncvt/vmerge/vmv C/C++ support

gcc/ChangeLog:

	* config/riscv/constraints.md (Wbr): Remove unused constraint.
	* config/riscv/predicates.md: Fix move operand predicate.
	* config/riscv/riscv-vector-builtins-bases.cc (class vnshift): New class.
	(class vncvt_x): Ditto.
	(class vmerge): Ditto.
	(class vmv_v): Ditto.
	(BASE): Ditto.
	* config/riscv/riscv-vector-builtins-bases.h: Ditto.
	* config/riscv/riscv-vector-builtins-functions.def (vsra): Ditto.
	(vsrl): Ditto.
	(vnsrl): Ditto.
	(vnsra): Ditto.
	(vncvt_x): Ditto.
	(vmerge): Ditto.
	(vmv_v): Ditto.
	* config/riscv/riscv-vector-builtins-shapes.cc (struct narrow_alu_def): Ditto.
	(struct move_def): Ditto.
	(SHAPE): Ditto.
	* config/riscv/riscv-vector-builtins-shapes.h: Ditto.
	* config/riscv/riscv-vector-builtins.cc (DEF_RVV_WEXTI_OPS): New variable.
	(DEF_RVV_WEXTU_OPS): Ditto
	* config/riscv/riscv-vector-builtins.def (x_x_w): Fix type for suffix.
	(v_v): Ditto.
	(v_x): Ditto.
	(x_w): Ditto.
	(x): Ditto.
	* config/riscv/riscv.cc (riscv_print_operand): Refine ASM printting rule.
	* config/riscv/vector-iterators.md (nmsac):New iterator.
	(nmsub): New iterator.
	* config/riscv/vector.md (@pred_merge<mode>): New pattern.
	(@pred_merge<mode>_scalar): New pattern.
	(*pred_merge<mode>_scalar): New pattern.
	(*pred_merge<mode>_extended_scalar): New pattern.
	(@pred_narrow_<optab><mode>): New pattern.
	(@pred_narrow_<optab><mode>_scalar): New pattern.
	(@pred_trunc<mode>): New pattern.