Implement "info chardev" command. (Gerd Hoffmann)

Implement "info chardev" command. (Gerd Hoffmann)

This patch makes qemu keep track of the character devices in use and
implements a "info chardev" monitor command to print a list.

qemu_chr_open() sticks the devices into a linked list now.  It got a new
argument (label), so there is a name for each device.  It also assigns a
filename to each character device.  By default it just copyes the
filename passed in.  Individual drivers can fill in something else
though.  qemu_chr_open_pty() sets the filename to name of the pseudo tty
allocated.

Output looks like this:

  (qemu) info chardev
  monitor: filename=unix:/tmp/run.sh-26827/monitor,server,nowait
  serial0: filename=unix:/tmp/run.sh-26827/console,server
  serial1: filename=pty:/dev/pts/5
  parallel0: filename=vc:640x480

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Patch adapted for qemu-xen-unstable by Stefano Stabellini.
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>