Merge remote-tracking branch 'remotes/rth-gitlab/tags/pull-tcg-20210104' into staging

Fix vector clear issue.
Fix riscv host shift issue.
Add tcg_gen_bswap_tl.

# gpg: Signature made Mon 04 Jan 2021 17:16:24 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-20210104:
  tcg: Add tcg_gen_bswap_tl alias
  tcg/riscv: Fix illegal shift instructions
  tcg: Use memset for large vector byte replication

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