aarch64: Use vec_perm_indices::new_shrunk_vector in aarch64_evpc_reencode

aarch64: Use vec_perm_indices::new_shrunk_vector in aarch64_evpc_reencode

While working on PERM related stuff, I can across that aarch64_evpc_reencode
was manually figuring out if we shrink the perm indices instead of
using vec_perm_indices::new_shrunk_vector; shrunk was added after reencode
was added.

Built and tested for aarch64-linux-gnu with no regressions.

gcc/ChangeLog:

	PR target/113822
	* config/aarch64/aarch64.cc (aarch64_evpc_reencode): Use
	vec_perm_indices::new_shrunk_vector instead of manually
	going through the indices.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>