xen: Make hvc0 the preferred console in domU

[Markus Armbruster <armbru@redhat.com>]

This makes the Xen console just work.  Before, you had to ask for it
on the kernel command line with console=hvc0

Signed-off-by: Markus Armbruster <armbru@redhat.com>

---
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 49e5358..df63185 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -25,6 +25,7 @@
 #include <linux/mm.h>
 #include <linux/page-flags.h>
 #include <linux/highmem.h>
+#include <linux/console.h>
 
 #include <xen/interface/xen.h>
 #include <xen/interface/physdev.h>
@@ -1209,6 +1210,9 @@ asmlinkage void __init xen_start_kernel(void)
 		? __pa(xen_start_info->mod_start) : 0;
 	boot_params.hdr.ramdisk_size = xen_start_info->mod_len;
 
+	if (!is_initial_xendomain())
+		add_preferred_console("hvc", 0, NULL);
+
 	/* Start the world */
 	start_kernel();
 }