dts: imx8mq-librem5: Add device trees that switch the built-in display to DCSS

Just to make testing and playing with different subsystems easier, not meant for
upstreaming.
2 jobs for dcss in 63 minutes and 38 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Build
passed #331547
librem5
build:aarch64

00:55:34

passed #331548
librem5:arm64
build:deb

01:03:38