rockchip: rk3399-puma: Increase environment size to 16 kiB.

On Puma we have the environment at an offset of 16 kiB.
On the eMMC this gives us 16 kiB for the environment before the SPL starts.
On the SPI NOR we also have 16 kiB until end of flash.
So let's increase the environment size from 8 kiB to its maximum
of 16 kiB for both MMC and SPI NOR.

Signed-off-by: Christoph Muellner <christoph.muellner@theobroma-systems.com>
Reviewed-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>