xen: 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/common/decompress.h

@@ -1,3 +1,6 @@
+#ifndef DECOMPRESS_H
+#define DECOMPRESS_H
+
 #ifdef __XEN__
 
 #include <xen/decompress.h>
@@ -22,3 +25,5 @@
 #define large_free free
 
 #endif
+
+#endif /* DECOMPRESS_H */

xen/common/efi/efi.h

@@ -1,3 +1,6 @@
+#ifndef EFI_EFI_H
+#define EFI_EFI_H
+
 #include <asm/efibind.h>
 #include <efi/efidef.h>
 #include <efi/efierr.h>
@@ -51,3 +54,5 @@ void free_ebmalloc_unused_mem(void);
 
 const void *pe_find_section(const void *image, const UINTN image_size,
                             const CHAR16 *section_name, UINTN *size_out);
+
+#endif /* EFI_EFI_H */

xen/common/event_channel.h

@@ -1,5 +1,8 @@
 /* Event channel handling private header. */
 
+#ifndef EVENT_CHANNEL_H
+#define EVENT_CHANNEL_H
+
 #include <xen/event.h>
 
 static inline unsigned int max_evtchns(const struct domain *d)
@@ -67,6 +70,8 @@ static inline void evtchn_fifo_destroy(struct domain *d)
 }
 #endif /* CONFIG_EVTCHN_FIFO */
 
+#endif /* EVENT_CHANNEL_H */
+
 /*
  * Local variables:
  * mode: C

xen/include/xen/pci_ids.h

@@ -1,3 +1,6 @@
+#ifndef XEN_PCI_IDS_H
+#define XEN_PCI_IDS_H
+
 #define PCI_VENDOR_ID_AMD                0x1022
 
 #define PCI_VENDOR_ID_NVIDIA             0x10de
@@ -11,3 +14,5 @@
 #define PCI_VENDOR_ID_BROADCOM           0x14e4
 
 #define PCI_VENDOR_ID_INTEL              0x8086
+
+#endif /* XEN_PCI_IDS_H */