CryptoPkg: Add some comments for API usage clarification.

This patch adds some comments for API usage clarification, and
adds one object initialization in X509ConstructCertificateStack
implementation to fix possible memory release issue.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Qin Long <qin.long@intel.com>
Reviewed-by: Ting Ye <ting.ye@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17671 6f19259b-4bc3-4df7-8a09-765794883524

CryptoPkg/Library/BaseCryptLib/Pk/CryptRsaExt.c

@@ -243,7 +243,9 @@ _Exit:
 }
 
 /**
-  Validates key components of RSA context.
+  Validates key components of RSA context. 
+  NOTE: This function performs integrity checks on all the RSA key material, so
+        the RSA key structure must contain all the private key data.
 
   This function validates key compoents of RSA context in following aspects:
   - Whether p is a prime