drm/arm/mali: Use drm_fb_cma_fbdev_init/fini()

Use drm_fb_cma_fbdev_init() and drm_fb_cma_fbdev_fini() which relies on
the fact that drm_device holds a pointer to the drm_fb_helper structure.
This means that the driver doesn't have to keep track of that.
Also use the drm_fb_helper functions directly.

Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Brian Starkey <brian.starkey@arm.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171115142001.45358-20-noralf@tronnes.org

drivers/gpu/drm/arm/malidp_drv.h

@@ -20,7 +20,6 @@
 
 struct malidp_drm {
 	struct malidp_hw_device *dev;
-	struct drm_fbdev_cma *fbdev;
 	struct drm_crtc crtc;
 	wait_queue_head_t wq;
 	atomic_t config_valid;