arm64: dts: qcom: msm8939: revert use of APCS mbox for RPM

Commit 22e4e43 ("arm64: dts: qcom: msm8939: Use mboxes
properties for APCS") broke the boot on msm8939 platforms.

The issue comes from the SMD driver failing to request the mbox
channel because of circular dependencies:
	1. rpm -> apcs1_mbox -> rpmcc (RPM_SMD_XO_CLK_SRC) -> rpm.
	2. rpm -> apcs1_mbox -> gcc -> rpmcc (RPM_SMD_XO_CLK_SRC) -> rpm
	3. rpm -> apcs1_mbox -> apcs2 -> gcc -> rpmcc (RPM_SMD_XO_CLK_SRC) -> rpm

To fix this issue let's switch back to using the deprecated
qcom,ipc property for the RPM node.

Fixes: 22e4e43 ("arm64: dts: qcom: msm8939: Use mboxes properties for APCS")
Signed-off-by: Fabien Parent <fabien.parent@linaro.org>
Link: https://lore.kernel.org/r/20240904-msm8939-rpm-apcs-fix-v1-1-b608e7e48fe1@linaro.org
Signed-off-by: Bjorn Andersson <andersson@kernel.org>

Author: Fabo

arch/arm64/boot/dts/qcom/msm8939.dtsi

@@ -248,7 +248,7 @@
 
 		smd-edge {
 			interrupts = <GIC_SPI 168 IRQ_TYPE_EDGE_RISING>;
-			mboxes = <&apcs1_mbox 0>;
+			qcom,ipc = <&apcs1_mbox 8 0>;
 			qcom,smd-edge = <15>;
 
 			rpm_requests: rpm-requests {