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 <[email protected]>
Reviewed-by: Dr. David Alan Gilbert <[email protected]>
Reviewed-by: Markus Armbruster <[email protected]>
Message-Id: <20190613153405[email protected]>
Signed-off-by: Markus Armbruster <[email protected]>