drm/hisilicon: Deleted the drm_device declaration

drm_framebuffer.h already declares struct drm_device, so there's no
need to declare it in hibmc_drm_drv.h

v2:
fixed spelling errors in commit message.

v3:
rewrite the commit message.

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/1601020086-43652-1-git-send-email-tiantao6@hisilicon.com