arm64: dts: qcom: msm8996: Use node references in db820c

Instead of mimicing the structure of the platform, reference nodes by
their label in apq8096-db820c.dtsi. Add labels in msm8996.dtsi where
necessary.
Acked-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

arch/arm64/boot/dts/qcom/msm8996.dtsi

@@ -1447,7 +1447,7 @@ gpu_speed_bin: gpu_speed_bin@133 {
 			};
 		};
 
-		phy@34000 {
+		pcie_phy: phy@34000 {
 			compatible = "qcom,msm8996-qmp-pcie-phy";
 			reg = <0x34000 0x488>;
 			#clock-cells = <1>;
@@ -1509,7 +1509,7 @@ pciephy_2: lane@37000 {
 			};
 		};
 
-		phy@7410000 {
+		usb3phy: phy@7410000 {
 			compatible = "qcom,msm8996-qmp-usb3-phy";
 			reg = <0x7410000 0x1c4>;
 			#clock-cells = <1>;