s390: Change get_dfp_rounding_mode to map IR rounding modes to
S390_DEP_ROUND_.. values in the range [8;15]. See comments in code.
Patch by Maran Pakkirisamy (maranp@linux.vnet.ibm.com).


git-svn-id: svn://svn.valgrind.org/vex/trunk@2679 8f6e269a-dfd6-0310-a8e1-e2731360e62c