firstboot: add actual reserved memory widget
    
    Memory reservation could fail, so add a new widget to show the
    actual reserved size. If crashkernel is set but reserved size is
    0, we still regard kdump is enabled, the actual reserved widget
    just show the reservation status.
    
    vivek: label with text "Memory Currently Reserved"
    
    Signed-off-by: Dave Young <dyoung@redhat.com>
    Reviewed-by: Vivek Goyal <vgoyal@redhat.com>