Merge remote-tracking branch 'remotes/rth/tags/tgt-openrisc-pull-request' into staging

Merge remote-tracking branch 'remotes/rth/tags/tgt-openrisc-pull-request' into staging

Convert openrisc to decodetree.py

# gpg: Signature made Mon 14 May 2018 23:25:40 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/tgt-openrisc-pull-request:
  target/openrisc: Merge disas_openrisc_insn
  target/openrisc: Convert dec_float
  target/openrisc: Convert dec_compi
  target/openrisc: Convert dec_comp
  target/openrisc: Convert dec_M
  target/openrisc: Convert dec_logic
  target/openrisc: Convert dec_mac
  target/openrisc: Convert dec_calc
  target/openrisc: Convert remainder of dec_misc insns
  target/openrisc: Convert memory insns
  target/openrisc: Convert branch insns
  target/openrisc: Start conversion to decodetree.py
  target-openrisc: Write back result before FPE exception

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