arm64: dts: qcom: sdm845: Add dpu to sdm845 dts file

DPU is short for the Display Processing Unit. It is the display
controller on Qualcomm SDM845 chips.

This change adds MDSS and DSI nodes to enable display on the
target device.

Changes in v2:
	 - Beefed up commit message
 	 - Use SoC specific compatibles for mdss and dpu (Rob H)
	 - Use assigned-clocks to set initial clock frequency(Rob H)
Changes in v3:
	 - added IOMMU node
 	 - Fix device naming (remove _phys)
	 - Use correct IRQ_TYPE in interrupt specifiers
Changes in v4:
 	 - move mdss node to preserve the unit address sort order
 	 - remove _clk suffix from dsi clocks
	 (both the comments are from Doug Anderson)
Changes in v5:
	- Keep the device status "disabled" by default (Bjorn Andersson)
	- Use MDSS_GDSC macro (Jordan)
	- Fix phy-names (Jordan)
	- List reg ranges in numerical order (Jordan)
Changes in v6:
	- Separating this patch out of the series
	- fix phy-names

Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>