Wrap a set of interesting paravirt_ops calls in a wrapper which makes
the callsites available for patching.  Unfortunately this is pretty
ugly because there's no way to get gcc to generate a function call,
but also wrap just the callsite itself with the necessary labels.

This patch supports functions with 0-4 arguments, and either void or
returning a value.  64-bit arguments must be split into a pair of
32-bit arguments (lower word first).  Small structures are returned in
registers.
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Zachary Amsden <zach@vmware.com>
Cc: Anthony Liguori <anthony@codemonkey.ws>