hw/display/cirrus_vga: Move "isa-cirrus-vga" device into a separate file

hw/display/cirrus_vga: Move "isa-cirrus-vga" device into a separate file

In downstream distros like RHEL we'd like to disable some of the "legacy"
devices of QEMU. The ISA version of the Cirrus VGA device is one of these
legacy devices. So let's make the build process a little bit more flexible
here by putting the Cirrus ISA code into a separate file which is only
included if both, CONFIG_VGA_CIRRUS and CONFIG_VGA_ISA are set.

Note that this disables "isa-cirrus-vga" for the ppc-softmmu and the
alpha-softmmu target since CONFIG_VGA_ISA is not set there. But I think
this is OK since these targets are only interested in the PCI variant
anyway.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-id: 1539339106-32427-1-git-send-email-thuth@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>