lguest: make hypercalls use the vcpu struct

this patch changes do_hcall() and do_async_hcall() interfaces (and obviously their
callers) to get a vcpu struct. Again, a vcpu services the hypercall, not the whole
guest

Signed-off-by: Glauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --cc drivers/lguest/core.c
Simple merge

diff --cc drivers/lguest/hypercalls.c
Simple merge

diff --cc drivers/lguest/lg.h
Simple merge

diff --cc drivers/lguest/x86/core.c
Simple merge