x86: cpu -- Don't fail if member is not present in image

When migrating from old images the particular xsave member
might not be present in core-* image, which is fine we
simply left data as initial zero state.

https://jira.sw.ru/browse/PSBM-89215



Signed-off-by: Cyrill Gorcunov <gorcunov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>