arm: [MVE intrinsics] Fix tuples field name (PR 118332)

The previous fix only worked for C, for C++ we need to add more
information to the underlying type so that
finish_class_member_access_expr accepts it.

We use the same logic as in aarch64's register_tuple_type for AdvSIMD
tuples.

This patch makes gcc.target/arm/mve/intrinsics/pr118332.c pass in C++
mode.

gcc/ChangeLog:

	PR target/118332
	* config/arm/arm-mve-builtins.cc (wrap_type_in_struct): Delete.
	(register_type_decl): Delete.
	(register_builtin_tuple_types): Use
	lang_hooks.types.simulate_record_decl.