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/Library/OpteeLib/OpteeSmc.h

@@ -7,8 +7,8 @@
 
 **/
 
-#ifndef _OPTEE_SMC_H_
-#define _OPTEE_SMC_H_
+#ifndef OPTEE_SMC_H_
+#define OPTEE_SMC_H_
 
 /* Returned in Arg0 only from Trusted OS functions */
 #define OPTEE_SMC_RETURN_OK                     0x0
@@ -47,4 +47,4 @@ typedef struct {
   UINT8   Data4[8];
 } RFC4122_UUID;
 
-#endif
+#endif // OPTEE_SMC_H_