target/s390x: Extract s390_get_bfp_rounding_mode()

target/s390x: Extract s390_get_bfp_rounding_mode()

For DIVIDE TO INTEGER it will be helpful to pass final-quotient
rounding mode around explicitly rather than setting it in fpu_status
implicitly. To facilitate this, extract a function for converting the
mask to the rounding mode.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-ID: <20260210214044.1174699-3-iii@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>