target/arm: Use pointers in neon tbl helper

target/arm: Use pointers in neon tbl helper

Rather than passing a regno to the helper, pass pointers to the
vector register directly.  This eliminates the need to pass in
the environment pointer and reduces the number of places that
directly access env->vfp.regs[].

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180119045438.28582-5-richard.henderson@linaro.org
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>