Setting root password fix - mixed

Based on commit: 263bc761767c3f316a09bbe47f1942c7444c7023

We're overriding system/system.mk because it's beeing executed before overlay files are copied.

BusyBox configuration also has to be altered, reference below.

-# CONFIG_CRYPTPW is not set
-# CONFIG_CHPASSWD is not set
+CONFIG_CRYPTPW=y
+CONFIG_CHPASSWD=y