Only *one* usermod directory can be specified, so the build command becomes something like:
make USER_C_MODULES=/path/to/pimoroni-pico/micropython/modules/
The `usermod.cmake` in the "modules" dir will then include all of the modules. Comment lines our here to disable them.
No need to configure anythign in `mpconfigport.h` since the defines are set by the `usermod.cmake` files.
Phil Howard