Merge remote-tracking branch 'remotes/rth/tags/pull-tcg-20180411' into staging

Handle read-modify-write i/o with icount

# gpg: Signature made Wed 11 Apr 2018 00:07:23 BST
# gpg:                using RSA key 64DF38E8AF7E215F
# gpg: Good signature from "Richard Henderson <richard.henderson@linaro.org>"
# Primary key fingerprint: 7A48 1E78 868B 4DB6 A85A  05C0 64DF 38E8 AF7E 215F

* remotes/rth/tags/pull-tcg-20180411:
  icount: fix cpu_restore_state_from_tb for non-tb-exit cases

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