microvm: use 3G split unconditionally

microvm: use 3G split unconditionally

Looks like the logic was copied over from q35.

q35 does this for backward compatibility, there is no reason to do this
on microvm though.  Also microvm doesn't need much mmio space, 1G is
more than enough.  Using an mmio window smaller than 1G is bad for
gigabyte alignment and hugepages though.  So split @ 3G unconditionally.

Signed-off-by: Gerd Hoffmann <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: Igor Mammedov <[email protected]>
Acked-by: Paolo Bonzini <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Message-id: 20200529073957[email protected]