AArch64: Fix single stepping of ERET instruction

Previously when single stepping through ERET instruction via GDB
would result in debugger entering the "next" PC after ERET instruction.
When debugging in kernel mode, this will also cause unintended behavior,
because debugger will try to access memory from EL0 point of view.

Signed-off-by: Jaroslaw Pelczar <j.pelczar@samsung.com>
Message-id: 001c01d32895$483027f0$d89077d0$@samsung.com
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/translate-a64.c

@@ -11348,6 +11348,7 @@ static void aarch64_tr_tb_stop(DisasContextBase *dcbase, CPUState *cpu)
         default:
             gen_a64_set_pc_im(dc->pc);
             /* fall through */
+        case DISAS_EXIT:
         case DISAS_JUMP:
             if (dc->base.singlestep_enabled) {
                 gen_exception_internal(EXCP_DEBUG);