Merge remote-tracking branch 'remotes/armbru/tags/pull-pflash-2019-03-26' into staging

Pflash and firmware configuration patches for 2019-03-26

# gpg: Signature made Tue 26 Mar 2019 07:21:13 GMT
# gpg:                using RSA key 3870B400EB918653
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>" [full]
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>" [full]
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-pflash-2019-03-26:
  pflash: Bury disabled code to limit device sizes
  pflash: Require backend size to match device, improve errors

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