target/arm: Ignore float_flag_input_denormal from fp_status_f16

target/arm: Ignore float_flag_input_denormal from fp_status_f16

When FZ is set, input_denormal exceptions are recognized, but this does
not happen with FZ16.  The softfloat code has no way to distinguish
these bits and will raise such exceptions into fp_status_f16.flags,
so ignore them when computing the accumulated flags.

Cc: qemu-stable@nongnu.org (3.0.1)
Reported-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Tested-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Message-id: 20180810193129.1556-3-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>