common: board_r: Drop initr_xen wrapper

Add a return value to xen_init and use it directly in the
post-relocation init sequence, rather than using a wrapper stub.

Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/xen.h

@@ -11,7 +11,7 @@
  * Map Xen memory pages, initialize event handler and xenbus,
  * setup the grant table.
  */
-void xen_init(void);
+int xen_init(void);
 
 /**
  * xen_fini() - Board cleanup before Linux kernel start