powerpc/kvm: Fix SMP=n build error in book3s_xics.c

Commit 34cb7954 "Convert ICS mutex lock to spin lock" added an
include of asm/spinlock.h, which does not work in the SMP=n case.

It should instead include linux/spinlock.h

Fixes: 34cb7954 ("KVM: PPC: Book3S HV: Convert ICS mutex lock to spin lock")
Acked-by: Paul Mackerras <paulus@samba.org>
Reviewed-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kvm/book3s_xics.c

@@ -12,6 +12,7 @@
 #include <linux/err.h>
 #include <linux/gfp.h>
 #include <linux/anon_inodes.h>
+#include <linux/spinlock.h>
 
 #include <asm/uaccess.h>
 #include <asm/kvm_book3s.h>
@@ -20,7 +21,6 @@
 #include <asm/xics.h>
 #include <asm/debug.h>
 #include <asm/time.h>
-#include <asm/spinlock.h>
 
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>