arm: mvebu: helios4: mmc: move environment before 1M

arm: mvebu: helios4: mmc: move environment before 1M

Store the environment before 1M into the block device.
This constant is easier to remember, saves a little space,
and is in line with what SolidRun's 2018.01-based fork does for the
clearfog.

Signed-off-by: Josua Mayer <[email protected]>
[ Aditya Prayoga:
* Port forward]
Signed-off-by: Aditya Prayoga <[email protected]>
Reviewed-by: Stefan Roese <[email protected]>
Tested-By: Dennis Gilmore <[email protected]>
Reviewed-By: Dennis Gilmore <[email protected]>
Signed-off-by: Stefan Roese <[email protected]>