Vlv2TbltDevicePkg: Add FileExplorerLib.inf to the dsc file

Vlv2TbltDevicePkg: Add FileExplorerLib.inf to the dsc file

Because SecureBootConfigDxe use FileExplorerLib now, but
FileExplorerLib is not in the dsc file of the package
that use SecureBootConfigDxe. Now add it to pass build.

Cc: David Wei <david.wei@intel.com>
Cc: Tim He <tim.he@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: David Wei <david.wei@intel.com>