fbdev: omapfb: Make FB_DEVICE dependency optional

fbdev: omapfb: Make FB_DEVICE dependency optional

omapfb provides several sysfs interfaces for framebuffer configuration
and debugging, but these are not required for the core driver.

Remove the hard dependency on CONFIG_FB_DEVICE and make sysfs support
optional by using dev_of_fbinfo() to obtain the backing device at runtime.
When FB_DEVICE is disabled, sysfs operations are skipped while the code
still builds and is type-checked.

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>