AArch64 disassembler failed to detect those undefined encodings on 
st1/st2/st3/st4.

This patch completed these checks.

OK for trunk and 2.24 branch?

Thanks.

-- 
Jiong


opcodes/

   * aarch64-dis.c (aarch64_ext_ldst_elemlist): Check H/S undefined 
instructions.

binutils/testsuite/

   * binutils-all/aarch64/aarch64.exp: New test driver for AArch64.
   * binutils-all/aarch64/unallocated-encoding.s: New testcase.
   * binutils-all/aarch64/unallocated-encoding.d: Ditto.