x86: cpu -- Detect and save fpu status in info

- externd compel_cpuinfo_t to keep all fpu information
   neded for xsaves mode

 - fetch xsaves data in compel_cpuid

All this will allow us to extend criu to support
avx-512 intructions.

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