drm/fb_helper: Create wrappers for fb_sys_read/write funcs

Some drm drivers populate their fb_ops with fb_sys_read/write fb sysfs
ops.

Create a drm_fb_helper function that wraps around these calls.

This is part of an effort to prevent drm drivers from calling fbdev
functions directly, in order to make fbdev emulation a top level drm
option.

v3:
- Fix kerneldoc errors

v2:
- Added kerneldocs
- Follow the drm way of aligning of arguments in func definitions
- Remove unnecessary checks for non NULL fb_info

Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/drm/drm_fb_helper.h

@@ -147,6 +147,11 @@ void drm_fb_helper_fill_fix(struct fb_info *info, uint32_t pitch,
 
 void drm_fb_helper_unlink_fbi(struct drm_fb_helper *fb_helper);
 
+ssize_t drm_fb_helper_sys_read(struct fb_info *info, char __user *buf,
+			       size_t count, loff_t *ppos);
+ssize_t drm_fb_helper_sys_write(struct fb_info *info, const char __user *buf,
+				size_t count, loff_t *ppos);
+
 int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info);
 
 int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper);