Merge remote-tracking branch 'remotes/xtensa/tags/20210403-xtensa' into staging

target/xtensa fixes for v6.0:

- make meson.build pick up all available xtensa core definitions;
- don't modify Makefile.objs in import_core.sh;
- add sed rule to import_core.sh to make xtensa_modules variable static.

# gpg: Signature made Sat 03 Apr 2021 17:08:41 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/20210403-xtensa:
  target/xtensa: make xtensa_modules static on import
  target/xtensa: fix meson.build rule for xtensa cores

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