xen/efi: Directly include needed headers

I discovered that some needed stuff is defined/declared in headers
which are not included directly. Currently it works but if somebody
remove required headers from currently included headers then build
will break. So, just in case directly include all needed headers.

Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
diff --git a/drivers/xen/efi.c b/drivers/xen/efi.c
index 31f618a..1f850c9 100644
--- a/drivers/xen/efi.c
+++ b/drivers/xen/efi.c
@@ -27,6 +27,8 @@
 #include <xen/interface/platform.h>
 #include <xen/xen.h>
 
+#include <asm/page.h>
+
 #include <asm/xen/hypercall.h>
 
 #define INIT_EFI_OP(name) \