Merge remote-tracking branch 'remotes/rth/tags/pull-dt-20190819' into staging

Implement parameter fields.
Push warning pragmas into the generated code.

# gpg: Signature made Mon 19 Aug 2019 16:14:41 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-dt-20190819:
  target/riscv: Remove redundant declaration pragmas
  decodetree: Suppress redundant declaration warnings
  decodetree: Allow !function with no input bits

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