x86, asmlinkage, paravirt: Add __visible/asmlinkage to xen paravirt ops

Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Link: http://lkml.kernel.org/r/1375740170-7446-13-git-send-email-andi@firstfloor.org


Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>