board: phytec: renaming of variables according to bootstd doc

Rename existing environment variables according to the bootstd doc.
Renamed variables are fdto_addr, bootenv_addr, fdt_addr and
fdt_file.

Signed-off-by: Benjamin Hahn <B.Hahn@phytec.de>
Signed-off-by: Daniel Schultz <d.schultz@phytec.de>
Reviewed-by: Wadim Egorov <w.egorov@phytec.de>
2 files changed