arm: Use vqmovun instead of vqshrun #0

binutils gas automatically produces vqmovun when vqshrun is used
with a zero shift.

This is required for building the armv8 assembly with the clang built-in
assembler.

Change-Id: Ie986978e4508a085e4e4c76f8db9a8a8394c4fec
1 file changed