arm/xen: don't inclide rwlock.h directly.

rwlock.h should not be included directly. Instead linux/splinlock.h
should be included. One thing it does is to break the RT build.

Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: xen-devel@lists.xenproject.org
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

arch/arm/xen/p2m.c

 #include <linux/bootmem.h>
 #include <linux/gfp.h>
 #include <linux/export.h>
-#include <linux/rwlock.h>
+#include <linux/spinlock.h>
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/dma-mapping.h>