modules: tf-m: fix build verbosity

Only set CMAKE_INSTALL_MESSAGE in a single location, remove the
unconditional overrides of the value in other locations.

This prevents dozens of rather pointless messages appearing in the build
log when CONFIG_TFM_BUILD_LOG_QUIET is set.
```
Installing: /home/jordan/code/workspace/build/nrf5340dk/...
```

Signed-off-by: Jordan Yates <jordan@embeint.com>