doc: announce vmbus API deprecation

All vmbus API functions are used internally by DPDK core and netvsc PMD.
It's not feasible or practical to use those APIs by the application.
Those APIs will become internal in DPDK 25.11.

Signed-off-by: Long Li <[email protected]>

Author: longlimsft

doc/guides/rel_notes/deprecation.rst

@@ -138,3 +138,7 @@ Deprecation Notices
   will be deprecated and subsequently removed in DPDK 24.11 release.
   Before this, the new port library API (functions rte_swx_port_*)
   will gradually transition from experimental to stable status.
+
+* bus/vmbus: Starting DPDK 25.11, all the vmbus API defined in
+  ``drivers/bus/vmbus/rte_bus_vmbus.h`` will become internal to DPDK.
+  Those API functions are used internally by DPDK core and netvsc PMD.