passthrough: don't call xc_deassign_device()

passthrough: don't call xc_deassign_device()

This series of patches modify the order of resetting/deassigning
device.

I modify the order of resetting/deassigning device like below.

  When guest OS shutdowns or a device is hotremoved.
   1. Xend resets devices.
   2. Xend deassigns devices.

Because if devices are deassigned before the reset, dom0 memory may be
broken by DMA

This patch modifies ioemu not to call xc_deassign_device()

Signed-off-by: Yuji Shimada <shimada-yxb@necst.nec.co.jp>