target/arm: Implement FCMP for fp16

target/arm: Implement FCMP for fp16

These where missed out from the rest of the half-precision work.

Cc: qemu-stable@nongnu.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180512003217.9105-9-richard.henderson@linaro.org
[rth: Diagnose lack of FP16 before fp_access_check]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>