target-mips: Correct MIPS16/microMIPS branch size calculation

Correct MIPS16/microMIPS branch size calculation in PC adjustment
needed:

- to set the value of CP0.ErrorEPC at the entry to the reset exception,

- for the purpose of branch reexecution in the context of device I/O.

Follow the approach taken in `exception_resume_pc' for ordinary, Debug
and NMI exceptions.

MIPS16 and microMIPS branches can be 2 or 4 bytes in size and that has
to be reflected in calculation.  Original MIPS ISA branches, which is
where this code originates from, are always 4 bytes long, just as all
original MIPS ISA instructions.

Signed-off-by: Nathan Froyd <froydnj@codesourcery.com>
Signed-off-by: Maciej W. Rozycki <macro@codesourcery.com>
Reviewed-by: Leon Alrae <leon.alrae@imgtec.com>
Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>

target-mips/translate.c

@@ -19439,7 +19439,8 @@ void cpu_state_reset(CPUMIPSState *env)
     if (env->hflags & MIPS_HFLAG_BMASK) {
         /* If the exception was raised from a delay slot,
            come back to the jump.  */
-        env->CP0_ErrorEPC = env->active_tc.PC - 4;
+        env->CP0_ErrorEPC = (env->active_tc.PC
+                             - (env->hflags & MIPS_HFLAG_B16 ? 2 : 4));
     } else {
         env->CP0_ErrorEPC = env->active_tc.PC;
     }

translate-all.c

@@ -1540,7 +1540,7 @@ void cpu_io_recompile(CPUState *cpu, uintptr_t retaddr)
        branch.  */
 #if defined(TARGET_MIPS)
     if ((env->hflags & MIPS_HFLAG_BMASK) != 0 && n > 1) {
-        env->active_tc.PC -= 4;
+        env->active_tc.PC -= (env->hflags & MIPS_HFLAG_B16 ? 2 : 4);
         cpu->icount_decr.u16.low++;
         env->hflags &= ~MIPS_HFLAG_BMASK;
     }