x86: boot - fix sparse warnings

Impact: make global variables static

Fix these sparse warnings:

 arch/x86/boot/video.c:233:3: warning: symbol 'saved' was not declared. Should it be static?
 arch/x86/boot/video-vga.c:37:13: warning: symbol 'video_vga' was not declared. Should it be static?

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>