BaseTools: Fix DSC override of Guided tool
    
    REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3359
    
    If the DSC file provides an override of a Guided tool path
    and/or Guided tool GUID value, then make sure the one from the
    DSC file is used if it is higher priority than the Guided tool
    in the tools_def.txt file.  This makes the Guided tool used by
    GenFds match the tool listed GuidedSectionTools.txt.
    
    Cc: Bob Feng <bob.c.feng@intel.com>
    Cc: Liming Gao <gaoliming@byosoft.com.cn>
    Cc: Yuwei Chen <yuwei.chen@intel.com>
    Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
    Reviewed-by: Bob Feng <bob.c.feng@intel.com>