arm: [MVE intrinsics] Fix moves of tuples (PR target/118131)

arm: [MVE intrinsics] Fix moves of tuples (PR target/118131)

Commit r15-6245-g4f4e13dd235b introduced new modes for MVE tuples, but
missed adding support for them in a few places.

Adding them to the list in arm_attr_length_move_neon is not sufficient
since we later face another ICE where the compiler does not know how
to split move of such data.

The patch therefore enhances the define_splits for OI and XI moves in
neon.md, via the introduction of new iterators.

In addition, it seems consistent to update output_move_neon such that
VALID_NEON_*_MODE are used only when TARGET_NEON.

gcc/ChangeLog:

	PR target/118131
	* config/arm/arm.cc (output_move_neon): Check TARGET_NEON as
	needed.
	(arm_attr_length_move_neon): Add support for V2x and V4x MVE tuple
	modes.
	* config/arm/iterators.md (VSTRUCT2, VSTRUCT4): New.
	* config/arm/neon.md: Use VSTRUCT2 instead of OI and VSTRUCT4
	instead of XI in define_split.