device/community/sdm845: disable serial console

Sooooo the kernel doesn't have async logging, and serial consoles are slow. the time is now!

I'm aware of one other developer (@amartinz) who has UART on an SDM845 device and makes use of it, it's probably more sensible for us to enable it rather than it being the default at this point.

Useful for !3884 (merged)

Maybe relevant to #1505 ?