BaseTools: Optimize VPD PCD value for the different SKUs

If VPD PCD value is same in the different SKUs, the different SKUs will
save the same offset for this PCD in VPD region. That means there is only
one PCD value copy in VPD region to save VPD space.

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