Add cirrus reset handler

The vga reset handler overwrites some cirrus registers, causing reboots
to corrupt cirrus state to the point that guests can only bring up 640x480
resolutions.

Fix by adding a dedicated cirrus reset handler (which calls the common vga
handler).

Signed-off-by: Avi Kivity <avi@redhat.com>


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6191 c046a42c-6fe2-441c-8c8c-71466251a162
