PReP machine and devices

* Cleanups for Raven PCI host bridge
* Removal of PReP machine and devices from qemu-system-ppcemb

# gpg: Signature made Mon 10 Feb 2014 16:19:03 GMT using RSA key ID 3E7E013F
# gpg: Good signature from "Andreas Färber <afaerber@suse.de>"
# gpg:                 aka "Andreas Färber <afaerber@suse.com>"

* remotes/afaerber/tags/prep-for-upstream:
  prep: Drop from ppcemb-softmmu
  raven: Use constant PCI_NUM_PINS instead of 4
  prep: Kill get_system_io() usage

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>