target/arm: Fix neon VTBL/VTBX for len > 1

target/arm: Fix neon VTBL/VTBX for len > 1

The helper function did not get updated when we reorganized
the vector register file for SVE.  Since then, the neon dregs
are non-sequential and cannot be simply indexed.

At the same time, make the helper function operate on 64-bit
quantities so that we do not have to call it twice.

Fixes: c39c2b9043e
Reported-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
[PMM: use aa32_vfp_dreg() rather than opencoding]
Message-id: 20201105171126.88014-1-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>