BaseTool: Filter out unused structure pcds

BaseTool: Filter out unused structure pcds

V2:
Fixed the issue that V1 adds new check
to the Pcds in the platform unused library INF files.
It breaks the existing platform.

V1?
The current code handle all the structure pcds
even if there is no module or library use them.
This patch is going to filter out the unused structure pcds.

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