target/xtensa improvements for v4.2:

- regenerate and reimport test_mmuhifi_c3 core;
- add virt machine.

# gpg: Signature made Wed 23 Oct 2019 23:56:42 BST
# gpg:                using RSA key 2B67854B98E5327DCDEB17D851F9CC91F83FA044
# gpg:                issuer "jcmvbkbc@gmail.com"
# gpg: Good signature from "Max Filippov <filippov@cadence.com>" [unknown]
# gpg:                 aka "Max Filippov <max.filippov@cogentembedded.com>" [full]
# gpg:                 aka "Max Filippov <jcmvbkbc@gmail.com>" [full]
# Primary key fingerprint: 2B67 854B 98E5 327D CDEB  17D8 51F9 CC91 F83F A044

* remotes/xtensa/tags/20191023-xtensa:
  hw/xtensa: add virt machine
  target/xtensa: regenerate and re-import test_mmuhifi_c3 core

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