Merge remote-tracking branch 'remotes/xtensa/tags/20151021-xtensa' into staging

Xtensa updates:

- fix register window overflow with l32e/s32e instructions;
- make MMU events logging dependent on CPU_LOG_MMU;
- attach FLASH to system I/O region on XTFPGA boards;
- implement depbits and l32nb instructions.

# gpg: Signature made Wed 21 Oct 2015 19:34:02 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/20151021-xtensa:
  target-xtensa: implement S32NB
  target-xtensa: implement depbits instruction
  target-xtensa: xtfpga: attach FLASH to system IO
  target-xtensa: use CPU_LOG_MMU for MMU event logging
  target-xtensa: add window overflow check to L32E/S32E

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