arm64: dts: qcom: sc8280xp: Add reference device

Add basic support for the SC8280XP reference device, which allows it to
boot to a shell (using EFIFB) with functional storage (UFS), USB,
keyboard, touchpad, touchscreen, backlight and remoteprocs.

The PMICs are, per socinfo, reused from other platforms. But given that
the address of the PMICs doesn't match other cases and that it's
desirable to label things according to the schematics a new dtsi file is
created to represent the reference combination of PMICs.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Johan Hovold <johan+linaro@kernel.org>
Link: https://lore.kernel.org/r/20220629041438.1352536-5-bjorn.andersson@linaro.org