target/arm/cpu.h: add additional float_status flags

target/arm/cpu.h: add additional float_status flags

Half-precision flush to zero behaviour is controlled by a separate
FZ16 bit in the FPCR. To handle this we pass a pointer to
fp_status_fp16 when working on half-precision operations. The value of
the presented FPCR is calculated from an amalgam of the two when read.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180227143852.11175-5-alex.bennee@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>