[RFC PATCH 0/2] arm64 kgdb fixes for single stepping

[minyard]

I got a bug report about using kgdb on arm64, and it turns out it was
fairly broken.  Patch 2 has a description of what was going on.  I am
using a Marvell 8100 board.

The following patches fix the problem, but probably not in the
best way.  They are what I hacked out to show the problems.

I am not quite sure how this will interact with kprobes and hardware
breakpoints which use the same code, but they would have been broken,
too, so this is not making them any worse.