x86, hyper: Change hypervisor detection order

x86, hyper: Change hypervisor detection order

Detect Xen before HyperV because in Viridian compatibility mode Xen
presents itself as HyperV.  Move Xen to the top since it seems more
likely that Xen would emulate VMware than vice versa.

Signed-off-by: Anupam Chanda <achanda@nicira.com>
Link: http://lkml.kernel.org/r/1310150570-26810-1-git-send-email-achanda@nicira.com
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Yaozu (Eddie) Dong <eddie.dong@intel.com>
Reviewed-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>