Vlv2TbltDevicePkg/SystemFirmwareDescriptor: Add Capsule Descriptor.

Vlv2TbltDevicePkg/SystemFirmwareDescriptor: Add Capsule Descriptor.

Add SystemFirmwareDescriptor for capsule update.
The PEIM extracts SystemFirmwareDescriptor info from FFS and reports
it via PCD.

Cc: David Wei <david.wei@intel.com>
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: David Wei <david.wei@intel.com>