target/mips: Fix single stepping

target/mips: Fix single stepping

As per an ancient comment in mips_tr_translate_insn about the
expectations of gdb, when restarting the insn in a delay slot
we also re-execute the branch.  Which means that we are
expected to execute two insns in this case.

This has been broken since 8b86d6d2580, where we forced max_insns
to 1 while single-stepping.  This resulted in an exit from the
translator loop after the branch but before the delay slot is
translated.

Increase the max_insns to 2 for this case.  In addition, bypass
the end-of-page check, for when the branch itself ends the page.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>