kasan: replicate x86 xen failure

Kasan does not work on Xen right now. It does work on bare metal
and kvm though. The reason for this is it does not have the same
setup work as done on early init for x86, as x86's bare metal early
init. It needs some work.

Additionally, you currently cannot disable kasan at run time and even
if you could we wouldn't know that Xen was the reason why this would
be failing. We have no way to annotate this at run time on bootup
for users or even developers. We'd want to annotate this to create
developer awareness over the requirements of such features which
require mucking with different init entries and to prevent code which
should be dead from running.

The work we'll do next will transform kasan to the use the table
init work, we'll also make use of the existing boot protocol subarch work
added through x86 boot protocol 2.08, and add capability support to
the init tables to be able to annotate when a general x86 feature
currenly lacks support for a boot run time environment, identified
through the subarch.

Current simulation which shows sucess on x86 and a replicated
issue when booting xen:

Bare metal simulation:

mcgrof@ergon ~/devel/table-init (git::master)$ ./main
Initializing x86 bare metal world
Number of init entries: 4
Initializing Memory ...
Completed initializing Memory !
Initializing PCI buses ...
Completed initializing PCI buses !
Initializing ACME(TM) Driver ...
Completed initializing ACME(TM) Driver !
Early init for Kasan...
Booting bare metal
Calling start_kernel()...
Calling setup_arch work for Kasan...

Xen simulation:

mcgrof@ergon ~/devel/table-init (git::master)$ ./main -x
Number of init entries: 4
Initializing Memory ...
Completed initializing Memory !
Initializing PCI buses ...
Completed initializing PCI buses !
Initializing ACME(TM) Driver ...
Completed initializing ACME(TM) Driver !
Initializing Xen Driver ...
Completed initializing Xen Driver !
Initializing Xen guest
Booting a Xen guest
Calling start_kernel()...
Kasan was not set up...
----------------------------------------------------------
BUG on kasan_init at kasan.c: 24

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>