ARM: dts: add rk3288 evaluation board

There exist 2 variants using either the act8846 or rk808 as pmic, while the
rest of the board stays the same.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Will Deacon <will.deacon@arm.com>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Tested-by: Doug Anderson <dianders@chromium.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>