Merge remote-tracking branch 'remotes/kraxel/tags/pull-fwcfg-20150414-1' into staging

fw_cfg: add documentation file (docs/specs/fw_cfg.txt)

# gpg: Signature made Tue Apr 14 12:22:20 2015 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-fwcfg-20150414-1:
  fw_cfg: add documentation file (docs/specs/fw_cfg.txt)

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