pci, pc, virtio bug fixes

This reverts PCI master abort support - we'll want it
eventually but it exposes too many core bugs to be safe for 1.7.
This also reverts a recent exec.c change that was an
attempt to work-around some of these core bugs.

Also included are small fixes in pc and virtio,
and a core loader fix for PPC bamboo.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

# gpg: Signature made Sun 10 Nov 2013 05:13:22 AM PST using RSA key ID D28D5469
# gpg: Can't check signature: public key not found

# By Michael S. Tsirkin (3) and others
# Via Michael S. Tsirkin
* mst/tags/for_anthony:
  Revert "exec: limit system memory size"
  Revert "hw/pci: partially handle pci master abort"
  loader: drop return value for rom_add_blob_fixed
  acpi-build: disable with -no-acpi
  virtio-net: only delete bh that existed
  Fix pc migration from qemu <= 1.5

Message-id: 1384159176-31662-1-git-send-email-mst@redhat.com
Signed-off-by: Anthony Liguori <aliguori@amazon.com>