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

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

introduce setup() and cleanup() which subsume the
ctx->restore.ops.{setup,cleanup}() calls and also
do memory alloc/free.

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