xen: arm: handle AArch32 userspace when dumping 64-bit guest state.

xen: arm: handle AArch32 userspace when dumping 64-bit guest state.

A 64-bit guest can still be in 32-bit mode when running userspace,
handle this case by dumping the correct 32-bit state.

Note that on ARM it is not possible to change mode without the help
of the next exception level, hence there is no way a 64-bit guest can
be running in 32-bit kernel modes.

This is part of CVE-2014-5147 / XSA-102.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Julien Grall <julien.grall@linaro.org>