libxc/save: introduce setup() and cleanup() on save

libxc/save: introduce setup() and cleanup() on save

introduce setup() and cleanup() which subsume the
ctx->save.ops.{setup,cleanup}() calls.
The SHADOW_OP_OFF hypercall is also included in the cleanup().

Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>
CC: Ian Campbell <Ian.Campbell@citrix.com>
CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
CC: Wei Liu <wei.liu2@citrix.com>
CC: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Campbell <Ian.Campbell@citrix.com>