doc: board: j721e_evm: Add documentation for firmware loading

Add documentation for loading firmwares to be used by remote cores in
the system including the environment variables that has to be set to
load the firmwares.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Link: https://lore.kernel.org/r/20210721155849.20994-21-kishon@ti.com
1 file changed