ArmPkg: Fix Ecc error 8003

This patch fixes the following Ecc reported error:
The #ifndef at the start of an include file should have
one postfix underscore, and no prefix underscore character

Some include guards have been modified to match the name of the
header file. Some comments have also been added on the closing
'#endif'.

Cc: Bret Barkelew <bret.barkelew@microsoft.com>
Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Sami Mujawar <sami.mujawar@arm.com>
Signed-off-by: Pierre Gondois <Pierre.Gondois@arm.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>

ArmPkg/Include/Library/OpteeLib.h

@@ -8,8 +8,8 @@
 
 **/
 
-#ifndef _OPTEE_H_
-#define _OPTEE_H_
+#ifndef OPTEE_LIB_H_
+#define OPTEE_LIB_H_
 
 /*
  * The 'Trusted OS Call UID' is supposed to return the following UUID for
@@ -117,4 +117,4 @@ OpteeInvokeFunction (
   IN OUT OPTEE_INVOKE_FUNCTION_ARG       *InvokeFunctionArg
   );
 
-#endif
+#endif // OPTEE_LIB_H_