As the original PineTab DT (which uses sun50i-a64-pinetab name) is only
for development samples, document this.
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20201224024138.19422-1-icenowy@aosc.io