rockchip: board: puma_rk3399: make env location selectable via Kconfig

The environment storage location is selectable via Kconfig. We support
eMMC, SD and SPI-NOR as location for U-Boot. This adds support to store
the environment in the SPI-NOR additional to the default eMMC location.

Signed-off-by: Klaus Goger <klaus.goger@theobroma-systems.com>
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>