Merge remote-tracking branch 'remotes/xtensa/tags/20180326-xtensa' into staging

Merge remote-tracking branch 'remotes/xtensa/tags/20180326-xtensa' into staging

target/xtensa fixes for 2.12:

- add .inc. to non-top level source file names under target/xtensa;
- fix #include <xtensa-isa.h> in the import_core.sh script;
- remove stray linux-user/xtensa/syscall.h;
- fix timers test.

# gpg: Signature made Mon 26 Mar 2018 22:40:20 BST
# 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/20180326-xtensa:
  target/xtensa: fix timers test
  linux-user/xtensa: remove stray syscall.h
  target/xtensa/import_core.sh: fix #include <xtensa-isa.h>
  target/xtensa: add .inc. to non-top level source file names

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