monitor: Extract completion declarations to 'monitor/hmp-completion.h'

Many files include "monitor/hmp.h", but few of them really need
the completion declarations: move them to a distinct header.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-Id: <20260320160811.28611-2-philmd@linaro.org>

net/net-hmp-cmds.c

@@ -16,6 +16,7 @@
 #include "qemu/osdep.h"
 #include "migration/misc.h"
 #include "monitor/hmp.h"
+#include "monitor/hmp-completion.h"
 #include "monitor/monitor.h"
 #include "net/net.h"
 #include "net/hub.h"