mvebu: Disable internal RTC on Linksys devices

The internal RTC does not work correctly on these Linksys boards based
on Marvell SoCs. It is off by 3 minutes in 10 minutes running, this
was reported by multiple users. On the Linksys Mamba device the device
tree comment says that no crystal is connected to the internal RTC, this
is probably also true for the other devices.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

target/linux/mvebu/patches-4.14/423-ARM-dts-armada-385-linksys-Disable-internal-RTC.patch

+From e1cac198fea08c31ec204bed84c279ab05d20389 Mon Sep 17 00:00:00 2001
+From: Hauke Mehrtens <hauke@hauke-m.de>
+Date: Sat, 17 Mar 2018 15:22:25 +0100
+Subject: ARM: dts: armada-385-linksys: Disable internal RTC
+
+The internal RTC does not work correctly on these Linksys boards based
+on Marvell SoCs. For me it only shows Wed Dec 31 23:59:59 1969 and for
+others it is off by 3 minutes in 10 minutes running, this was reported
+by multiple users. On the Linksys Mamba device the device tree comment
+says that no crystal is connected to the internal RTC, this is probably
+also true for the other devices.
+
+Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
+---
+ arch/arm/boot/dts/armada-385-linksys.dtsi | 5 +++++
+ 1 file changed, 5 insertions(+)
+
+--- a/arch/arm/boot/dts/armada-385-linksys.dtsi
++++ b/arch/arm/boot/dts/armada-385-linksys.dtsi
+@@ -302,3 +302,8 @@
+ 	status = "okay";
+ 	usb-phy = <&usb3_1_phy>;
+ };
++
++&rtc {
++	/* No crystal connected to the internal RTC */
++	status = "disabled";
++};