drm: Drop ioctl->cmd_drv

ioctl->cmd_drv is pointless and we can just as well stick the full ioctl
definition into ioctl->cmd.

Cc: Jakob Bornecrantz <jakob@vmware.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>