[nrf fromlist] boards: nordic: nrf54h20dk: ipc to cpusys with unbound

Unbound feature in IPC with cpusys will be enabled by default.
This is needed to enable IPC link renewal.
If unbound is not needed then it can be disabled in overlay,
sysctrl will detect if it is present.

Upstream PR #: 94646

Signed-off-by: Łukasz Stępnicki <[email protected]>
(cherry picked from commit 6872776)

Author: lstnl

boards/nordic/nrf54h20dk/nrf54h20dk_nrf54h20-ipc_conf.dtsi

@@ -32,6 +32,7 @@
 
 		cpuapp_cpusys_ipc: ipc-2-12 {
 			compatible = "zephyr,ipc-icmsg";
+			unbound = "enable";
 			status = "disabled";
 			dcache-alignment = <32>;
 			mboxes = <&cpuapp_bellboard 6>,
@@ -56,6 +57,7 @@
 
 		cpurad_cpusys_ipc: ipc-3-12 {
 			compatible = "zephyr,ipc-icmsg";
+			unbound = "enable";
 			status = "disabled";
 			dcache-alignment = <32>;
 			mboxes = <&cpurad_bellboard 6>,