target/arm/helper: pass explicit fpst to set_rmode

target/arm/helper: pass explicit fpst to set_rmode

As the rounding mode is now split between FP16 and the rest of
floating point we need to be explicit when tweaking it. Instead of
passing the CPU env we now pass the appropriate fpst pointer directly.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180227143852.11175-6-alex.bennee@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>