configs/seli8: enable field fail-safe u-boot update

configs/seli8: enable field fail-safe u-boot update

Field fail-safe u-boot update for pg-wcom-ls102x designs is introduced
with patch 81fb05e.

This patch enables already added support by:
 - Defining default u-boot build as bootpackage (factory) image.
 - Defining u-boot update image location according to the SELI8 NOR layout.
 - Extending mtd partitions according defined SELI8 NOR layout.

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