phycore_imx8mp: Move environment from include/config to board

Move the environment into the board directory and convert it from a C
header to a text file. Sort the variables alphabetically.
No functional changes.

Signed-off-by: Leonard Anderweit <l.anderweit@phytec.de>
Reviewed-by: Teresa Remmet <t.remmet@phytec.de>
Tested-by: Teresa Remmet <t.remmet@phytec.de>