fbdev: sstfb: Make CONFIG_FB_DEVICE optional

fbdev: sstfb: Make CONFIG_FB_DEVICE optional

The sstfb driver currently depends on CONFIG_FB_DEVICE to create sysfs
entries and access info->dev. This patch wraps the relevant code blocks
with #ifdef CONFIG_FB_DEVICE, allowing the driver to be built and used
even if CONFIG_FB_DEVICE is not selected.

The sysfs setting only controls the VGA pass-through state and is not
required for the display to work correctly.
(See: http://vogonswiki.com/index.php/VGA_passthrough_cable
for more information.)

Added some fixes from Thomas Zimmermann.

Signed-off-by: Gonzalo Silvalde Blanco <gonzalo.silvalde@gmail.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Helge Deller <deller@gmx.de>