xen/arm: add inclusion guards

MISRA C Directive 4.10 states that:
"Precautions shall be taken in order to prevent the contents of a
header file being included more than once".

Add inclusion guards where missing to address violations of the
guideline.

Signed-off-by: Federico Serafini <federico.serafini@bugseng.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/arm/efi/efi-boot.h

@@ -3,6 +3,10 @@
  * is intended to be included by common/efi/boot.c _only_, and
  * therefore can define arch specific global variables.
  */
+
+#ifndef ARM_EFI_BOOT_H
+#define ARM_EFI_BOOT_H
+
 #include <xen/device_tree.h>
 #include <xen/libfdt/libfdt.h>
 #include <asm/setup.h>
@@ -1003,6 +1007,8 @@ static void __init efi_arch_flush_dcache_area(const void *vaddr, UINTN size)
     __flush_dcache_area(vaddr, size);
 }
 
+#endif /* ARM_EFI_BOOT_H */
+
 /*
  * Local variables:
  * mode: C

xen/arch/arm/include/asm/efibind.h

@@ -1,2 +1,7 @@
+#ifndef ARM_EFIBIND_H
+#define ARM_EFIBIND_H
+
 #include <xen/types.h>
 #include <asm/arm64/efibind.h>
+
+#endif /* ARM_EFIBIND_H */