SignedCapsulePkg/CapsulePkg.dec: Add capsule related definition.

SignedCapsulePkg/CapsulePkg.dec: Add capsule related definition.

1) Add capsule related GUID.
   EdkiiSystemFmpCapsule
2) Add capsule related library.
   EdkiiSystemCapsuleLib
   IniParsingLib
   PlatformFlashAccessLib
3) Add EDKII system capsule related DynamicEx PCD
   PcdEdkiiSystemFirmwareImageDescriptor
   PcdEdkiiSystemFirmwareFileGuid
   NOTE: We use DynamicEx here because the update driver may be in
   the capsule FMP, instead of system firmware.
   The update driver MUST use the PCD info produced system firmware.
4) Add Test key file PCD
   These PCDs indicate the GUID of FFS which contains test key file.

Cc: Feng Tian <feng.tian@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Chao Zhang <chao.b.zhang@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Michael Kinney <michael.d.kinney@intel.com>
Tested-by: Michael Kinney <michael.d.kinney@intel.com>