drm: drivers/char/drm/: make some functions static

From: Adrian Bunk <bunk@stusta.de>

This patch makes some needlessly global functions static.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Dave Airlie <airlied@linux.ie>