target-i386: update fp status fix

This patch introduces cpu_set_fpuc() function, which changes fpuc field
of the CPU state and calls update_fp_status() function.
These calls update status of softfloat library and prevent bugs caused
by non-coherent rounding settings of the FPU and softfloat.

v2 changes:
 * Added missed calls and intoduced setter function (as suggested by TeLeMan)

Reviewed-by: TeLeMan <geleman@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
