drm/rockchip: add missing header dependencies

We get 2 warnings when building kernel with W=1:
drivers/gpu/drm/rockchip/rockchip_drm_fbdev.c:130:5: warning: no previous prototype for 'rockchip_drm_fbdev_init' [-Wmissing-prototypes]
drivers/gpu/drm/rockchip/rockchip_drm_fbdev.c:173:6: warning: no previous prototype for 'rockchip_drm_fbdev_fini' [-Wmissing-prototypes]

In fact, these functions are declared
in drivers/gpu/drm/rockchip/rockchip_drm_fbdev.h,
so this patch adds missing header dependencies.
Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1474789109-22010-1-git-send-email-baoyou.xie@linaro.org

drivers/gpu/drm/rockchip/rockchip_drm_fbdev.c

@@ -20,6 +20,7 @@
 #include "rockchip_drm_drv.h"
 #include "rockchip_drm_gem.h"
 #include "rockchip_drm_fb.h"
+#include "rockchip_drm_fbdev.h"
 
 #define PREFERRED_BPP		32
 #define to_drm_private(x) \