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/IndustryStandard/ArmMmSvc.h

@@ -6,8 +6,8 @@
 *
 **/
 
-#ifndef __ARM_MM_SVC_H__
-#define __ARM_MM_SVC_H__
+#ifndef ARM_MM_SVC_H_
+#define ARM_MM_SVC_H_
 
 /*
  * SVC IDs to allow the MM secure partition to initialise itself, handle
@@ -44,4 +44,4 @@
 #define SPM_MAJOR_VERSION                     0
 #define SPM_MINOR_VERSION                     1
 
-#endif
+#endif // ARM_MM_SVC_H_