PR rtl-optimization/119046: aarch64: Fix PARALLEL mode for vec_perm DUP expansion

The PARALLEL created in aarch64_evpc_dup is used to hold the lane number.
It is not appropriate for it to have a vector mode.
Other such uses use VOIDmode.
Do this here as well.
This avoids the risk of generic code treating the PARALLEL as trapping when it
has floating-point mode.

Bootstrapped and tested on aarch64-none-linux-gnu.

Signed-off-by: Kyrylo Tkachov <ktkachov@nvidia.com>

	PR rtl-optimization/119046
	* config/aarch64/aarch64.cc (aarch64_evpc_dup): Use VOIDmode for
	PARALLEL.