Merge remote-tracking branch 'remotes/xtensa/tags/20181030-xtensa' into staging

Merge remote-tracking branch 'remotes/xtensa/tags/20181030-xtensa' into staging

target/xtensa: support for bFLT binaries

- add support for bFLT binaries for target/xtensa
- fix per-architecture target_flat.h customization
- fix initial stack pointer for bFLT

# gpg: Signature made Tue 30 Oct 2018 18:27:42 GMT
# gpg:                using RSA key 51F9CC91F83FA044
# gpg: Good signature from "Max Filippov <filippov@cadence.com>"
# gpg:                 aka "Max Filippov <max.filippov@cogentembedded.com>"
# gpg:                 aka "Max Filippov <jcmvbkbc@gmail.com>"
# Primary key fingerprint: 2B67 854B 98E5 327D CDEB  17D8 51F9 CC91 F83F A044

* remotes/xtensa/tags/20181030-xtensa:
  linux-user/flatload: fix initial stack pointer alignment
  linux-user: xtensa: enable bFLT support

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