checkpoint: Add dumping of FPU state

The dumping of FPU state is done with help of ptrace
facility. There are two cases which we need to handle
depending on which features are available on host machine

1) The dump via ptrace(PTRACE_GETFPREGS ...)

   In this case the kernel will use fxsave approach
   inside the kenrel and provides us back the data
   encoded in i387_fxsave_struct format.

2) The dump via ptrace(PTRACE_GETREGSET ...)

   In this case the kernel will use xsave approach
   inside the kernel and provides us back the data
   encoded in xsave_struct format.

In any case we decode data and save it in protobuf format.
This is why core.proto file has been extended to keep new
entries.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>