target/arm: Don't allow Thumb Neon insns without FEATURE_NEON

target/arm: Don't allow Thumb Neon insns without FEATURE_NEON

We were accidentally permitting decode of Thumb Neon insns even if
the CPU didn't have the FEATURE_NEON bit set, because the feature
check was being done before the call to disas_neon_data_insn() and
disas_neon_ls_insn() in the Arm decoder but was omitted from the
Thumb decoder.  Push the feature bit check down into the called
functions so it is done for both Arm and Thumb encodings.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20200430181003.21682-3-peter.maydell@linaro.org