pg-wcom-ls102xa: Include <config.h> in the board file

Given that this file references CFG_* defines, we need to be explicit in
our inclusion of config.h, so that these will be defined.

Reviewed-by: Aleksandar Gerasimovski <aleksandar.gerasimovski@hitacienergy.com>
Signed-off-by: Tom Rini <trini@konsulko.com>