BootMaintenanceMangerUiLib: Save mode info for later use.
    
    In current code, we use different output modes for boot phase
    and setup phase. When split BootMaintenanceMangerUiLib from
    UiApp code, we not add logic to save the boot phase mode info
    which will be used later. This change add this logic.
    
    Contributed-under: TianoCore Contribution Agreement 1.0
    Signed-off-by: Eric Dong <eric.dong@intel.com>
    Reviewed-by: Liming Gao <liming.gao@intel.com>