Without this, after the first build of wrpc-sw the ppsi
configuration was never changed.

So if you built e.g. "gsi_defconfig" and then reconfigure
for "gsi_pdelay_defconfig" you'll get no pdelay in there.

For me, and the next maintainers of ppsi, the new configuration option
CONFIG_PPSI_FORCE_CONFIG can be unset in order to test with personale
changes in ppsi configuration.
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>