T1042RDB_PI_NAND_SECURE_BOOT: Guard t104xrdb SPL env code

We can only configure and set the environment in SPL when we have a
particular environment location set that is not "nowhere" like it is in
SECURE_BOOT designs.  Update the code to reflect that.

Cc: Priyanka Jain <priyanka.jain@nxp.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>