Add minimal DT files for the Amlogic P20x development boards, based on
the Amlogic S905/GXBB SoC.

Cc: Andreas Färber <afaerber@suse.de>
Cc: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>