xen/x86: make "earlyprintk=xen" work for HVM/PVH DomU

xenboot_write_console() is dealing with these quite fine so I don't see
why xenboot_console_setup() would return -ENOENT in this case.

Adjust documentation accordingly.

Signed-off-by: Jan Beulich <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Juergen Gross <[email protected]>

Author: jbeulich

Documentation/admin-guide/kernel-parameters.txt

@@ -1255,7 +1255,7 @@
 			The VGA and EFI output is eventually overwritten by
 			the real console.
 
-			The xen output can only be used by Xen PV guests.
+			The xen option can only be used in Xen domains.
 
 			The sclp output can only be used on s390.
 

drivers/tty/hvc/hvc_xen.c

@@ -607,10 +607,8 @@ static int __init xenboot_console_setup(struct console *console, char *string)
 {
 	static struct xencons_info xenboot;
 
-	if (xen_initial_domain())
+	if (xen_initial_domain() || !xen_pv_domain())
 		return 0;
-	if (!xen_pv_domain())
-		return -ENODEV;
 
 	return xencons_info_pv_init(&xenboot, 0);
 }