target/arm: Clear CONTROL_S.SFPA in SG insn if FPU present

target/arm: Clear CONTROL_S.SFPA in SG insn if FPU present

If the floating point extension is present, then the SG instruction
must clear the CONTROL_S.SFPA bit. Implement this.

(On a no-FPU system the bit will always be zero, so we don't need
to make the clearing of the bit conditional on ARM_FEATURE_VFP.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20190416125744.27770-8-peter.maydell@linaro.org