xen kconfig: relax INPUT_XEN_KBDDEV_FRONTEND deps

PV-on-HVM guests may want to use the xen keyboard/mouse frontend, but
they don't use the xen frame buffer frontend. For this case it doesn't
make much sense for INPUT_XEN_KBDDEV_FRONTEND to depend on
XEN_FBDEV_FRONTEND. The opposite direction always makes more sense, i.e.
if you're using xenfb, then you'll want xenkbd. Switch the dependencies.

Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
index d83e967..269b299 100644
--- a/drivers/video/Kconfig
+++ b/drivers/video/Kconfig
@@ -2269,6 +2269,7 @@
 	select FB_SYS_IMAGEBLIT
 	select FB_SYS_FOPS
 	select FB_DEFERRED_IO
+	select INPUT_XEN_KBDDEV_FRONTEND
 	select XEN_XENBUS_FRONTEND
 	default y
 	help