Merge remote-tracking branch 'remotes/rth/tags/pull-tcg-20201008' into staging

Extend maximum gvec vector size
Fix i386 avx2 dupi
Fix mips host user-only write detection
Misc cleanups.

# gpg: Signature made Thu 08 Oct 2020 13:55:22 BST
# 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/tags/pull-tcg-20201008:
  accel/tcg: Fix computing of is_write for MIPS
  tcg: Remove TCG_TARGET_HAS_cmp_vec
  tcg/optimize: Fold dup2_vec
  tcg: Fix generation of dupi_vec for 32-bit host
  tcg/i386: Fix dupi for avx2 32-bit hosts
  tcg: Remove TCGOpDef.used
  tcg: Move some TCG_CT_* bits to TCGArgConstraint bitfields
  tcg: Remove TCG_CT_REG
  tcg: Move sorted_args into TCGArgConstraint.sort_index
  tcg: Drop union from TCGArgConstraint
  tcg: Adjust simd_desc size encoding

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