vl.c: daemonize before guest memory allocation

memory allocated for guest before QEMU is daemonized and then mapped
later in guest's address space after it is daemonized, leads to EPT
violation and QEMU aborts.

To avoid this and similar issues switch to daemonized mode early
before applying/processing other options.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
