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/Chipset/AArch64Mmu.h

@@ -6,8 +6,8 @@
 *
 **/
 
-#ifndef __AARCH64_MMU_H_
-#define __AARCH64_MMU_H_
+#ifndef AARCH64_MMU_H_
+#define AARCH64_MMU_H_
 
 //
 // Memory Attribute Indirection register Definitions
@@ -194,5 +194,5 @@
 
 // Uses LPAE Page Table format
 
-#endif // __AARCH64_MMU_H_
+#endif // AARCH64_MMU_H_