MdeModulePkg: Variable: Update PCR[7] measure for new TCG spec

MdeModulePkg: Variable: Update PCR[7] measure for new TCG spec

Measure DBT into PCR[7] when it is updated between initial measure and
ExitBootService. Measure "SecureBoot" change after PK update.
Spec version : TCG PC Client PFP 00.37. http://www.trustedcomputinggroup.org/wp-content/uploads/PC-ClientSpecific_Platform_Profile_for_TPM_2p0_Systems_v21.pdf

Cc: Star Zeng <star.zeng@intel.com>
Cc: Yao Jiewen <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Chao Zhang <chao.b.zhang@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Yao Jiewen <jiewen.yao@intel.com>