Merge remote-tracking branch 'remotes/rth-gitlab/tags/pull-tcg-20201210' into staging

Merge remote-tracking branch 'remotes/rth-gitlab/tags/pull-tcg-20201210' into staging

Split CpusAccel for tcg variants

# gpg: Signature made Fri 11 Dec 2020 01:07:33 GMT
# gpg:                using RSA key 7A481E78868B4DB6A85A05C064DF38E8AF7E215F
# gpg:                issuer "richard.henderson@linaro.org"
# gpg: Good signature from "Richard Henderson <richard.henderson@linaro.org>" [full]
# Primary key fingerprint: 7A48 1E78 868B 4DB6 A85A  05C0 64DF 38E8 AF7E 215F

* remotes/rth-gitlab/tags/pull-tcg-20201210:
  accel/tcg: rename tcg-cpus functions to match module name
  accel/tcg: split tcg_start_vcpu_thread
  accel/tcg: split CpusAccel into three TCG variants

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