x86: early PV on HVM features initialization.

Initialize basic pv on hvm features adding a new Xen HVM specific
hypervisor_x86 structure.

Don't try to initialize xen-kbdfront and xen-fbfront when running on HVM
because the backends are not available.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Sheng Yang <sheng@linux.intel.com>
Signed-off-by: Yaozu (Eddie) Dong <eddie.dong@intel.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
diff --git a/drivers/input/xen-kbdfront.c b/drivers/input/xen-kbdfront.c
index e140816..ebb1190 100644
--- a/drivers/input/xen-kbdfront.c
+++ b/drivers/input/xen-kbdfront.c
@@ -339,7 +339,7 @@
 
 static int __init xenkbd_init(void)
 {
-	if (!xen_domain())
+	if (!xen_pv_domain())
 		return -ENODEV;
 
 	/* Nothing to do if running in dom0. */