pc: resizeable ROM blocks

This makes ROM blocks resizeable.  This infrastructure is required for other
functionality we have queued.

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

# gpg: Signature made Thu 08 Jan 2015 11:19:24 GMT using RSA key ID D28D5469
# gpg: Good signature from "Michael S. Tsirkin <mst@kernel.org>"
# gpg:                 aka "Michael S. Tsirkin <mst@redhat.com>"

* remotes/mst/tags/for_upstream:
  acpi-build: make ROMs RAM blocks resizeable
  memory: API to allocate resizeable RAM MR
  arch_init: support resizing on incoming migration
  exec: qemu_ram_alloc_resizeable, qemu_ram_resize
  exec: split length -> used_length/max_length
  exec: cpu_physical_memory_set/clear_dirty_range
  memory: add memory_region_set_size

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