armv8: ls1046afrwy: Define CONFIG_ENV_ADDR for QSPI Boot

Defines CONFIG_ENV_ADDR for QSPI Boot which specifies the start
address of the flash sector containing the environment. It fixes
the issue that bootcmd is always set as default at bootup.

Signed-off-by: Alison Wang <alison.wang@nxp.com>
Reviewed-by: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>