BaseTools:StructurePCD value display incorrect in "Not used" section.

BaseTools:StructurePCD value display incorrect in "Not used" section.

StructurePCD value display incorrect in "Not used" section,
that the value defined in structure does not show.

StructurePCD will not display in "Not Used" section if
main structure not define in dsc and pcd not in inf

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Zhiju.Fan <zhijux.fan@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>