arm/pci-designware: Fix MISRA violations

* Move includes inside the header guards (D4.10)
 * Use NULL in preference to 0 (R11.9)

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Nicola Vetrini <nicola.vetrini@bugseng.com>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>

xen/arch/arm/pci/pci-designware.c

@@ -285,7 +285,7 @@ void __iomem *dw_pcie_child_map_bus(struct pci_host_bridge *bridge,
                                     bridge->child_cfg->phys_addr, busdev,
                                     bridge->child_cfg->size);
     if ( ret )
-        return 0;
+        return NULL;
 
     return bridge->child_cfg->win + where;
 }

xen/arch/arm/pci/pci-designware.h

@@ -6,12 +6,11 @@
  * Based on xen/arch/arm/pci/pci-host-generic.c
  */
 
-#include <xen/pci.h>
-#include <xen/init.h>
-
 #ifndef __PCI_DESIGNWARE_H__
 #define __PCI_DESIGNWARE_H__
 
+#include <xen/pci.h>
+#include <xen/init.h>
 
 #define PCIE_ATU_VIEWPORT               0x900
 #define PCIE_ATU_REGION_OUTBOUND        0