arm64: dts: sdm845: add oneplus6/6t devices

Add initial support for the OnePlus 6 (enchilada) and 6T (fajita) based
on the sdm845-mtp DT with the following functionality:

 * Touch
 * Display
 * GPU
 * Wlan and Bluetooth
 * USB peripheral mode
 * Remoteproc

Reviewed-by: Konrad Dybcio <konrad.dybcio@somainline.org>
Signed-off-by: Caleb Connolly <caleb@connolly.tech>
Link: https://lore.kernel.org/r/20210114203057.64541-2-caleb@connolly.tech
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>