phycore_imx8mm: Switch to using env text files

Move the environment into the board directory and convert header to a
txt file. In addition, this patch also applies following changes:

- Change default nfsroot path to /srv/nfs due to compliance with Linux
FHS 3.0.

- Rename specific variables as stated in the bootstd documentation.
Renamed variables:
	fdt_addr => fdt_addr_r
	fdt_file => fdtfile

Signed-off-by: Yunus Bas <y.bas@phytec.de>
2 files changed