target-mips: do not allow Status.FR=0 mode in 64-bit FPU

Status.FR bit must be ignored on write and read as 1 when an implementation of
Release 6 of the Architecture in which a 64-bit floating point unit is
implemented.
Signed-off-by: NLeon Alrae <leon.alrae@imgtec.com>
Reviewed-by: NYongbok Kim <yongbok.kim@imgtec.com>

target-mips/translate.c

@@ -17951,6 +17951,12 @@ void cpu_state_reset(CPUMIPSState *env)
         }
     }
 #endif
+    if ((env->insn_flags & ISA_MIPS32R6) &&
+        (env->active_fpu.fcr0 & (1 << FCR0_F64))) {
+        /* Status.FR = 0 mode in 64-bit FPU not allowed in R6 */
+        env->CP0_Status |= (1 << CP0St_FR);
+    }
+
     compute_hflags(env);
     cs->exception_index = EXCP_NONE;
 }