dt-bindings: pci: qcom: Document PCIe bindings for SM8250 SoC

Document the PCIe DT bindings for SM8250 SoC. The PCIe IP is similar to
the one used on SDM845, hence just add the compatible along with the
optional "atu" register region.

Link: https://lore.kernel.org/r/20201208121402.178011-2-mani@kernel.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/pci/qcom,pcie.txt

@@ -13,6 +13,7 @@
 			- "qcom,pcie-ipq8074" for ipq8074
 			- "qcom,pcie-qcs404" for qcs404
 			- "qcom,pcie-sdm845" for sdm845
+			- "qcom,pcie-sm8250" for sm8250
 
 - reg:
 	Usage: required
@@ -27,6 +28,7 @@
 			- "dbi"	   DesignWare PCIe registers
 			- "elbi"   External local bus interface registers
 			- "config" PCIe configuration space
+			- "atu"    ATU address space (optional)
 
 - device_type:
 	Usage: required
@@ -131,7 +133,7 @@
 			- "slave_bus"	AXI Slave clock
 
 -clock-names:
-	Usage: required for sdm845
+	Usage: required for sdm845 and sm8250
 	Value type: <stringlist>
 	Definition: Should contain the following entries
 			- "aux"		Auxiliary clock
@@ -206,7 +208,7 @@
 			- "ahb"			AHB reset
 
 - reset-names:
-	Usage: required for sdm845
+	Usage: required for sdm845 and sm8250
 	Value type: <stringlist>
 	Definition: Should contain the following entries
 			- "pci"			PCIe core reset