drm: cleanup modesetting ioctls, one param per line

Since this already confused me once when adding addfb2.1, let's clean up
the header to split params one per line.

Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>