arm64: dts: fsl: librem5: Drop imx8_som node

We don't need the imx8_som node drop it.

Signed-off-by: Angus Ainslie (Purism) <angus@akkea.ca>
2 jobs for imx8-4.18-fixes in 39 minutes and 8 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
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passed #13680
librem5
build:aarch64:Image

00:39:08

passed #13681
librem5
build:aarch64:deb

00:24:40