Merge remote-tracking branch 'remotes/rth/tags/pull-tcg-20151021' into staging

Collected tcg backend patches

# gpg: Signature made Wed 21 Oct 2015 22:34:28 BST using RSA key ID 4DD0279B
# gpg: Good signature from "Richard Henderson <rth7680@gmail.com>"
# gpg:                 aka "Richard Henderson <rth@redhat.com>"
# gpg:                 aka "Richard Henderson <rth@twiddle.net>"

* remotes/rth/tags/pull-tcg-20151021:
  cpu-exec: Add "nochain" debug flag
  tcg/mips: Support r6 SEL{NE, EQ}Z instead of MOVN/MOVZ
  tcg/mips: Support r6 multiply/divide encodings
  tcg/mips: Support r6 JR encoding
  tcg/mips: Add use_mips32r6_instructions definition
  disas/mips: Add R6 jr/jr.hb to disassembler
  tcg-opc.h: Simplify insn_start def
  tcg/ppc: Prefer mask over andi.
  tcg/ppc: Revise goto_tb implementation
  tcg/ppc: Adjust exit_tb for change in prologue placement

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