ARM: dts: qcom: ipq8064: add specific dtsi with smb208 rpm regulators

Add specific ipq8064 dtsi with smb208 rpm regulators.

Qcom advise to use this configuration but it's not mandatory and OEM
can decide to implement their own regulators.
smb208 regulators are used to scale CPU voltage, L2 cache voltage and
Ubi32 cores.

There regulators are controlled by rpm and to correctly works gsbi4-i2c
require to be NEVER disabled or rpm will reject any regulator change
request.

Signed-off-by: Christian Marangi <[e-mail]>
Tested-by: Jonathan McDowell <[e-mail]>
Signed-off-by: Bjorn Andersson <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/arm/boot/dts/qcom-ipq8064-smb208.dtsi

···
+// SPDX-License-Identifier: GPL-2.0
+
+#include "qcom-ipq8064.dtsi"
+
+&rpm {
+	smb208_regulators: regulators {
+		compatible = "qcom,rpm-smb208-regulators";
+
+		smb208_s1a: s1a {
+			regulator-min-microvolt = <1050000>;
+			regulator-max-microvolt = <1150000>;
+
+			qcom,switch-mode-frequency = <1200000>;
+		};
+
+		smb208_s1b: s1b {
+			regulator-min-microvolt = <1050000>;
+			regulator-max-microvolt = <1150000>;
+
+			qcom,switch-mode-frequency = <1200000>;
+		};
+
+		smb208_s2a: s2a {
+			regulator-min-microvolt = < 800000>;
+			regulator-max-microvolt = <1250000>;
+
+			qcom,switch-mode-frequency = <1200000>;
+		};
+
+		smb208_s2b: s2b {
+			regulator-min-microvolt = < 800000>;
+			regulator-max-microvolt = <1250000>;
+
+			qcom,switch-mode-frequency = <1200000>;
+		};
+	};
+};