drm/exynos: drop DRM_AUTH from DRM_RENDER_ALLOW ioctls

The authentication can be circumvented, by design, by using the render
node.

From the driver POV there is no distinction between primary and render
nodes, thus we can drop the token.

Cc: Inki Dae <inki.dae@samsung.com>
Cc: Joonyoung Shim <jy0922.shim@samsung.com>
Cc: Seung-Woo Kim <sw0312.kim@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Acked-by: Inki Dae <inki.dae@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190527081741.14235-4-emil.l.velikov@gmail.com