x86: cpu -- Add ability to ignore xsaves

Currently even if kernel supports compact xsave frame a user
can disable it by passing noxsaves argument as a boot option.
Thus cpuid instruction will report its presence but in real
it gonna be masked from kernel pov. Lets do the same and
allow a user to mask it via --cpu-cap=noxsaves option
(valid for x86 only).

Reviewed-by: Dmitry Safonov <0x7f454c46@gmail.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>