fb: Add dev_of_fbinfo() helper for optional sysfs support

Add dev_of_fbinfo() to return the framebuffer struct device when
CONFIG_FB_DEVICE is enabled, or NULL otherwise.

This allows fbdev drivers to use sysfs interfaces via runtime checks
instead of CONFIG_FB_DEVICE ifdefs, keeping the code clean while
remaining fully buildable.

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

Author: nehudesi

include/linux/fb.h

@@ -623,6 +623,15 @@ static inline void unlock_fb_info(struct fb_info *info)
 	mutex_unlock(&info->lock);
 }
 
+static inline struct device *dev_of_fbinfo(const struct fb_info *info)
+{
+#ifdef CONFIG_FB_DEVICE
+	return info->dev;
+#else
+	return NULL;
+#endif
+}
+
 static inline void __fb_pad_aligned_buffer(u8 *dst, u32 d_pitch,
 					   u8 *src, u32 s_pitch, u32 height)
 {