ARM: dts: sd_600eval: Fix eMMC lockup issue

This board locks up if we stress test the eMMC, as the regulator s4 is
unable to supply enough current for all the peripherials attached to it.
As this supply is wired up to most of the peripherials including DDR,
it resulted in such lockup.

This patch fixes this issue by setting s4 regulator correctly with
Auto power mode.
Reported-by: NSrinivas Kandagatla <srinivas.kandagatla@linaro.org>
[Srinivas Kandagatla: rewrote the change log]
Tested-by: NGirish Sharma <girish.sharma@einfochips.com>
Signed-off-by: NParth Pancholi <parth.pancholi@einfochips.com>
Signed-off-by: NAndy Gross <andy.gross@linaro.org>

arch/arm/boot/dts/qcom-apq8064-arrow-sd-600eval.dts

 #include "qcom-apq8064-v2.0.dtsi"
 #include "qcom-apq8064-arrow-sd-600eval-pins.dtsi"
 #include <dt-bindings/gpio/gpio.h>
+#include <dt-bindings/mfd/qcom-rpm.h>
 
 / {
 	model = "Arrow Electronics, APQ8064 SD_600eval";
@@ -82,7 +83,8 @@
 				s4 {
 					regulator-min-microvolt	= <1800000>;
 					regulator-max-microvolt	= <1800000>;
-					qcom,switch-mode-frequency = <3200000>;
+					qcom,switch-mode-frequency = <1600000>;
+					qcom,force-mode = <QCOM_RPM_FORCE_MODE_AUTO>;
 					bias-pull-down;
 					regulator-always-on;
 				};