Do you want a customized boot screen or do you just want the LCD to be turned on when the booting process is finished and MM is active?
In my case I have a PIR-sensor with a relay to trigger my LCD when a person is in front of the mirror. The script for the PIR/relay is loaded when the Pi boots up. That means the LCD stays off until the script is loaded, so the first thing I see is MM loading the modules.
For the splashscreen you can have a look here (haven’t tried it myself).