drm: move MODULE_PARM_DESC to other file

We moved the module options from drm_drv.c to drm_irq.c in 18882995
('drm: Move vblank related module options into drm_irq.c').  Let's move
the MODULE_PARM_DESC()s as well so they're together.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20160108110045.GF32195@mwanda


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>