Merge remote-tracking branch 'remotes/xtensa/tags/20160523-opencores_eth' into staging

opencores_eth cleanups:
- use mii.h
- reduce stack usage in open_eth_start_xmit.

# gpg: Signature made Mon 23 May 2016 20:14:20 BST using RSA key ID F83FA044
# gpg: Good signature from "Max Filippov <max.filippov@cogentembedded.com>"
# gpg:                 aka "Max Filippov <jcmvbkbc@gmail.com>"

* remotes/xtensa/tags/20160523-opencores_eth:
  hw/net/opencores_eth: Allocating Large sized arrays to heap
  hw/net/opencores_eth: use mii.h

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