Merge remote-tracking branch 'remotes/kraxel/tags/vga-20190524-pull-request' into staging

ramfb: misc improvements.

# gpg: Signature made Fri 24 May 2019 09:56:59 BST
# gpg:                using RSA key 4CB6D8EED3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>" [full]
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>" [full]
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>" [full]
# Primary key fingerprint: A032 8CFF B93A 17A7 9901  FE7D 4CB6 D8EE D3E8 7138

* remotes/kraxel/tags/vga-20190524-pull-request:
  hw/display/ramfb: initialize fw-config space with xres/ yres
  hw/display/ramfb: lock guest resolution after it's set
  hw/display/ramfb: fix guest memory un-mapping

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