Convert the vga-isa-mm device away from the old_mmio
MemoryRegion accessors.

This device is only used by the MIPS 'jazz' boards
"magnum" and "pica61".

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Hervé Poussineau <hpoussin@reactos.org>
Tested-by: Hervé Poussineau <hpoussin@reactos.org>
Message-id: 20180802155147.1863-2-peter.maydell@linaro.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>