xen: Add basic hooks for PVH in current code

Add the hooks to current code needed for Xen PVH. They will be filled
with code later when the related functionality is being added.

loader/i386/linux.c needs to include machine/kernel.h now as it needs
to get GRUB_KERNEL_USE_RSDP_ADDR from there. This in turn requires to
add an empty kernel.h header for some i386 platforms (efi, coreboot,
ieee1275, xen) and for x86_64 efi.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Tested-by: Hans van Kranenburg <hans@knorrie.org>

grub-core/kern/xen/init.c

@@ -564,6 +564,10 @@ grub_machine_init (void)
 			   + GRUB_KERNEL_MACHINE_MOD_GAP,
 			   GRUB_KERNEL_MACHINE_MOD_ALIGN);
 
+#ifdef GRUB_MACHINE_XEN_PVH
+  grub_xen_setup_pvh ();
+#endif
+
   grub_xen_setup_gnttab ();
 
 #ifdef GRUB_MACHINE_XEN