configs: j721e_evm.h: Sync J721e environment configuration with AM65x

Some of the environment configuration in AM65x is not available in
J721e due to additions on one but not the other. These two platforms
are similar enough these common definitions should be factored out
to a common area, prepare for this by synchronizing them.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>