console: add graphic_console_set_hwops

Add a function to allow display emulations to switch the hwops
function pointers.  This is useful for devices which have two
completely different operation modes.  Typical case is the vga
compatibility mode vs. native mode in qxl and the upcoming
virtio-vga device.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
qxl: use graphic_console_set_hwops

Simply switch function pointers when entering/leaving vga mode.
Allows to remove wrapper functions which do nothing but dispatch
calls depending on the current qxl mode.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Merge remote-tracking branch 'remotes/spice/tags/pull-spice-20140929-1' into staging

add and use graphic_console_set_hwops

# gpg: Signature made Mon 29 Sep 2014 11:18:37 BST using RSA key ID D3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>"
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>"
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>"

* remotes/spice/tags/pull-spice-20140929-1:
  qxl: use graphic_console_set_hwops
  console: add graphic_console_set_hwops

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