km: ls102xa: add missing define for PRAM regions

In our designs we reserve PRAM area at the end of the RAM, and in order
this area to be visible and taken into account by the u-boot memory mgmt
CONFIG_PRAM has to be defined.

Signed-off-by: Aleksandar Gerasimovski <aleksandar.gerasimovski@hitachi-powergrids.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>