board: ti: j784s4: Add boot environment variables

Add env file with necessary boot variables.

[ added env files ]
Signed-off-by: Neha Malcom Francis <n-francis@ti.com>
[ cleaned up the env files ]
Signed-off-by: Manorit Chawdhry <m-chawdhry@ti.com>
Signed-off-by: Apurva Nandan <a-nandan@ti.com>
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com> # AM69-SK