Added an optional SplitFspBin.py path argument

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1691



What was done:
- an optional 7th argument was added to RebaseAndPatchFspBinBaseAddress.py
- updated lincense on RebaseAndPatchFspBinBaseAddress.py
- replace \\ with os independent os.sep

Cc: Michael Kubacki <michael.a.kubacki@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Ankit Sinha <ankit.sinha@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>

Signed-off-by: Agyeman <prince.agyeman@intel.com>
Reviewed-by: Michael Kubacki <michael.a.kubacki@intel.com>
Tested-by: Michael Kubacki <michael.a.kubacki@intel.com>