monitor: Split out monitor/hmp.c

monitor: Split out monitor/hmp.c

Move HMP infrastructure from monitor/misc.c to monitor/hmp.c. This is
code that can be shared for all targets, so compile it only once.

The amount of function and particularly extern variables in
monitor_int.h is probably a bit larger than it needs to be, but this way
no non-trivial code modifications are needed. The interfaces between HMP
and the monitor core can be cleaned up later.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20190613153405.24769-12-kwolf@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Comment reformatted to make checkpatch.pl happy, #include <dirent.h>
moved to fix Windows build, superfluous #include dropped]
Signed-off-by: Markus Armbruster <armbru@redhat.com>