fbdev: sh_mobile_lcdc: Make FB_DEVICE dependency optional

fbdev: sh_mobile_lcdc: Make FB_DEVICE dependency optional

The sh_mobile_lcdc driver exposes overlay configuration via sysfs, but the
core driver does not require CONFIG_FB_DEVICE.

Make overlay sysfs optional so that the driver can build and operate
even when FB_DEVICE is disabled. The kernel naturally ignores the
missing attribute group, preserving buildability and type safety.

Suggested-by: Helge Deller <deller@gmx.de>
Signed-off-by: Chintan Patel <chintanlike@gmail.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Helge Deller <deller@gmx.de>