1. Change 0 == Length style to Length == 0

2. Clean BasePeCoff library instance, only keep one copy PeCoffLoaderEx.c file for IA32, X64 and IPF arch
3. Clean the confused comments

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@5927 6f19259b-4bc3-4df7-8a09-765794883524

MdePkg/Library/BaseLib/String.c

@@ -289,7 +289,7 @@ StrnCmp (
   IN      UINTN                     Length
   )
 {
-  if (0 == Length) {
+  if (Length == 0) {
     return 0;
   }
 
@@ -1151,7 +1151,7 @@ AsciiStrnCpy (
 {
   CHAR8                             *ReturnValue;
 
-  if (0 == Length) {
+  if (Length == 0) {
     return Destination;
   }
 
@@ -1430,7 +1430,7 @@ AsciiStrnCmp (
   IN      UINTN                     Length
   )
 {
-  if (0 == Length) {
+  if (Length == 0) {
     return 0;
   }