configs: lx2160a: Define ENV_ADDR value

CONFIG_ENV_ADDR helps in picking environment from flash before DDR init.
Define the value as 0x20500000 for lx2160ardb and lx2160aqds.

Signed-off-by: Kuldeep Singh <kuldeep.singh@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>