oprofile, x86: Using struct stack_frame for 64bit processes dump

Removing unnecessary struct frame_head and replacing it with
struct stack_frame.

The struct stack_frame is already defined and used in other places
in kernel, so there's no reason to define new structure.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Robert Richter <robert.richter@amd.com>