add DisplayState->idle (Samuel Thibault)

add DisplayState->idle (Samuel Thibault)

Add idle field to DisplayState struct, so drivers can figure
the display is idle and take advantage of that.

The xen framebuffer driver will use this to communicate the
idle state to the guest, so it knows it can stop doing updates
to a virtual display which is invisible anyway.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Samuel Thibault <samuel.thibault@eu.citrix.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5056 c046a42c-6fe2-441c-8c8c-71466251a162