target-arm: Add AArch64 gdbstub support

target-arm: Add AArch64 gdbstub support

We want to be able to debug AArch64 guests. So let's add the respective gdb
stub functions and xml descriptions that allow us to do so.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: John Rigby <john.rigby@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1378235544-22290-12-git-send-email-peter.maydell@linaro.org
Message-id: 1368505980-17151-6-git-send-email-john.rigby@linaro.org
[PMM: dropped unused fp regs XML for now; moved 64 bit only functions
 to new gdbstub64.c; these are hooked up in AArch64CPU, not via
 ifdefs in ARMCPU]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>