target/arm: Diagnose UNALLOCATED in disas_simd_three_reg_same_fp16

target/arm: Diagnose UNALLOCATED in disas_simd_three_reg_same_fp16

This fprintf+assert has been in place since the beginning.
It is after to the fp_access_check, so we need to move the
check up.  Fold that in to the pairwise filter.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20210604183506.916654-4-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>