Creates a module that exports Xen Hypervisor attributes to sysfs. The

Creates a module that exports Xen Hypervisor attributes to sysfs. The
module has a tri-state configuration so it can be a loadable module.

Views the hypervisor as hardware device, uses sysfs as  a scripting
interface for user space tools that need these attributes.

Some user space apps, particularly for systems management, need to
know if their kernel is running in a virtual machine and if so in
what type of virtual machine. This property is contained in the
file /sys/hypervisor/type.

The file hypervisor_sysfs.c creates a generic  hypervisor subsystem
that can be linked to by any hypervisor. The file xen_sysfs.c exports
the xen-specific attributes.

Signed-off-by: Mike D. Day <ncmike@us.ibm.com>