Merge remote-tracking branch 'remotes/xtensa/tags/20190122-xtensa' into staging

target/xtensa: zero overhead loops rework/helpers split

- change xtensa zero overhead loops implementation to avoid invalidation
  of TBs corresponding to previous loop body when a new loop is
  encountered;
- extract helper function groups from op_helper.c and move them into
  separate source files: exc_helper.c (exception helpers), win_helper.c
  (windowed registers helpers), fpu_helper.c (floating point helpers),
  mmu_helper.c (memory management helpers) and dbg_helper.c (native debug
  helpers).

# gpg: Signature made Tue 22 Jan 2019 18:44:17 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/20190122-xtensa:
  target/xtensa: move non-HELPER functions to helper.c
  target/xtensa: drop dump_state helper
  target/xtensa: extract interrupt and exception helpers
  target/xtensa: extract debug helpers
  target/xtensa: extract MMU helpers
  target/xtensa: extract windowed registers helpers
  target/xtensa: extract FPU helpers
  target/xtensa: rework zero overhead loops implementation

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