mips64: finetune mips_dirtyhelper_calculate_FCSR

Several MIPS32 Revision 2 instructions also belong to Revision 1 of MIPS64.
Modifing parts of mips_dirtyhelper_calculate_FCSR to be active for MIPS64R1.

This fixes none/tests/mips64/round when Valgrind is compiled for MIPS64 R1.


git-svn-id: svn://svn.valgrind.org/vex/trunk@2774 8f6e269a-dfd6-0310-a8e1-e2731360e62c