Merge remote-tracking branch 'remotes/kraxel/tags/pull-fw_cfg-20151020-1' into staging

fw_cfg: add dma interface, add strings via cmdline.

# gpg: Signature made Tue 20 Oct 2015 07:07:34 BST using RSA key ID D3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>"
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>"
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>"

* remotes/kraxel/tags/pull-fw_cfg-20151020-1:
  fw_cfg: Define a static signature to be returned on DMA port reads
  Enable fw_cfg DMA interface for x86
  Enable fw_cfg DMA interface for ARM
  Implement fw_cfg DMA interface
  fw_cfg DMA interface documentation
  fw_cfg: document fw_cfg_modify_iXX() update functions
  fw_cfg: insert string blobs via qemu cmdline

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