target-mips: Add missing calls to synchronise SoftFloat status

Add missing calls to synchronise the SoftFloat status with the CP1.FSCR:

+ for the rounding and flush-to-zero modes upon processor reset,

+ for the flush-to-zero mode on FSCR updates through the GDB stub.

Refactor code accordingly and remove the redundant RESTORE_ROUNDING_MODE
macro.

Backports commit bb962386b82c1b0e9e12fdb6b9bb62106bf1f822 from qemu

qemu/target-mips/cpu.h

@@ -771,6 +771,19 @@ target_ulong exception_resume_pc (CPUMIPSState *env);
 extern unsigned int ieee_rm[];
 int ieee_ex_to_mips(int xcpt);
 
+static inline void restore_rounding_mode(CPUMIPSState *env)
+{
+    set_float_rounding_mode(ieee_rm[env->active_fpu.fcr31 & 3],
+                            &env->active_fpu.fp_status);
+}
+
+static inline void restore_flush_mode(CPUMIPSState *env)
+{
+    set_flush_to_zero((env->active_fpu.fcr31 & (1 << 24)) != 0,
+                      &env->active_fpu.fp_status);
+}
+
+
 static inline void cpu_get_tb_cpu_state(CPUMIPSState *env, target_ulong *pc,
                                         target_ulong *cs_base, int *flags)
 {

qemu/target-mips/op_helper.c

@@ -2283,18 +2283,6 @@ unsigned int ieee_rm[] = {
     float_round_down
 };
 
-static inline void restore_rounding_mode(CPUMIPSState *env)
-{
-    set_float_rounding_mode(ieee_rm[env->active_fpu.fcr31 & 3],
-                            &env->active_fpu.fp_status);
-}
-
-static inline void restore_flush_mode(CPUMIPSState *env)
-{
-    set_flush_to_zero((env->active_fpu.fcr31 & (1 << 24)) != 0,
-                      &env->active_fpu.fp_status);
-}
-
 target_ulong helper_cfc1(CPUMIPSState *env, uint32_t reg)
 {
     target_ulong arg1 = 0;

qemu/target-mips/translate.c

@@ -19826,6 +19826,8 @@ void cpu_state_reset(CPUMIPSState *env)
     }
 
     compute_hflags(env);
+    restore_rounding_mode(env);
+    restore_flush_mode(env);
     cs->exception_index = EXCP_NONE;
 }