BaseTools: Adjust StructurePcd List Order.

BaseTools: Adjust StructurePcd List Order.

Currently StructurePcd.dsc have the list order issue. For a Pcd
with several elements, the list indexs are used to distinguish
these elements like this:

PcdName.name.offset_name[0]|0x0
PcdName.name.offset_name[10]|0x0
PcdName.name.offset_name[11]|0x0
...
PcdName.name.offset_name[2]|0x0
...

However, the index is not strictly sorted by decimal numerical order,
which is not user friendly. One more sort rule for index is added to
the current rules to support for decimal numerical order in this patch.

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Signed-off-by: Yuwei Chen <yuwei.chen@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>