monitor: Create monitor-internal.h with common definitions

Before we can split monitor/misc.c, we need to create a header file that
contains the common definitions that will be used by multiple source
files.

For a start, add the type definitions for Monitor, MonitorHMP and
MonitorQMP and their dependencies. We'll add functions as needed when
splitting monitor/misc.c.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20190613153405.24769-10-kwolf@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Header guard symbol tidied up, superfluous #include dropped, FIXME in
hmp_change() resolved]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 3c7d366..15f21c3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1918,6 +1918,7 @@
 Human Monitor (HMP)
 M: Dr. David Alan Gilbert <dgilbert@redhat.com>
 S: Maintained
+F: monitor/monitor-internal.h
 F: monitor/misc.c
 F: monitor/hmp*
 F: hmp.h
@@ -2040,6 +2041,7 @@
 QMP
 M: Markus Armbruster <armbru@redhat.com>
 S: Supported
+F: monitor/monitor-internal.h
 F: monitor/qmp*
 F: monitor/misc.c
 F: docs/devel/*qmp-*