monitor: Move {hmp, qmp}.c to monitor/{hmp, qmp}-cmds.c

monitor: Move {hmp, qmp}.c to monitor/{hmp, qmp}-cmds.c

Now that we have a monitor/ subdirectory, let's move hmp.c and qmp.c
from the root directory there. As they contain implementations of
monitor commands, rename them to {hmp,qmp}-cmds.c, so that {hmp,qmp}.c
are free for the HMP and QMP infrastructure.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20190613153405.24769-9-kwolf@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>