rockchip: rk3399-puma: Move ENV_OFFSET to end of SPI NOR.

rockchip: rk3399-puma: Move ENV_OFFSET to end of SPI NOR.

Puma SoMs have a 4 MB SPI NOR flash.
Therefore we can move the environment to the end of the flash
(4 MiB - 16 kiB) in order to not overlap with SPL.

Reported-by: Jakob Unterwurzacher <jakob.unterwurzacher@theobroma-systems.com>
Signed-off-by: Christoph Muellner <christoph.muellner@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>