arm: [MVE intrinsics] fix vdup iterator

This patch fixes a bug where the mode iterator for mve_vdup<mode>
should be MVE_VLD_ST instead of MVE_vecs: V2DI and V2DF (thus vdup.64)
are not supported by MVE.

2024-07-02  Jolen Li  <jolen.li@arm.com>
	    Christophe Lyon  <christophe.lyon@arm.com>

	gcc/
	* config/arm/mve.md (mve_vdup<mode>): Fix mode iterator.