x86/boot/video: Move the 'video_segment' variable to video.c

video.c is the only real user of the 'video_segment' variable,
so move it to video.c and make it static.

Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Martin Mares <mj@ucw.cz>
Link: http://lkml.kernel.org/r/1422123092-28750-1-git-send-email-kuleshovmail@gmail.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>