BaseTools: Customize deepcopy function.

BaseTools: Customize deepcopy function.

https://bugzilla.tianocore.org/show_bug.cgi?id=1288

This patch is one of build tool performance improvement
series patches.

This patch is going to customize the deepcopy function for
SkuClass, PcdClassObject and python dictionary.

python deepcopy copy everything of a object, but for our current
usage we just need to copy the data we care about recursively.

By implementing __deepcopy__ for SkuClass, PcdClassObject, we can customize
deepcopy function for them.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: BobCF <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>