arm64: dts: rockchip: Disable display for NanoPi R2S

arm64: dts: rockchip: Disable display for NanoPi R2S

NanoPi R2S is headless, so rightly does not enable any of the display
interface hardware, which currently provokes an obnoxious error in the
boot log from the fake DRM device failing to find anything to bind to.
It probably isn't *too* hard to obviate the fake device shenanigans
entirely with a bit of driver reshuffling, but for now let's just
disable it here to shut up the spurious error.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/c4553dfad1ad6792c4f22454c135ff55de77e2d6.1611186099.git.robin.murphy@arm.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>