drm/gma500: Remove unnecessary include statements

Remove unnecessary include statements from framebuffer.c. No
functional changes.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230313151610.14367-2-tzimmermann@suse.de