configs: ls1012a: Reduce CONFIG_ENV_SIZE to 0x2000

configs: ls1012a: Reduce CONFIG_ENV_SIZE to 0x2000

All LS1012A board variants have same CONFIG_ENV_SECT_SIZE and
CONFIG_ENV_SIZE values. If both config values are same, flash
environment cannot be saved. Since, CONFIG_ENV_SECT_SIZE needs to be
same as that of flash sector size, this entry cannot be changed.
Reduce CONFIG_ENV_SIZE value to 0x2000. This also helps in making config
value aligned with other boards environemt size.

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