of: Make devtree_lock declaration private

Sparc is the only place devtree_lock is used outside of drivers/of/.
Move the devtree_lock declaration into of_private.h and Sparc's prom.h
so pulling in spinlock.h to of.h can be avoided for everything besides
Sparc.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Rob Herring <[e-mail]>

arch/sparc/include/asm/prom.h

···
 #include <linux/mutex.h>
 #include <linux/atomic.h>
 #include <linux/irqdomain.h>
+#include <linux/spinlock.h>
 
 #define of_compat_cmp(s1, s2, l)	strncmp((s1), (s2), (l))
 #define of_prop_cmp(s1, s2)		strcasecmp((s1), (s2))
 #define of_node_cmp(s1, s2)		strcmp((s1), (s2))
+
+extern raw_spinlock_t devtree_lock;
 
 struct of_irq_controller {
 	unsigned int	(*irq_build)(struct device_node *, unsigned int, void *);

drivers/of/of_private.h

···
 #define OF_ROOT_NODE_SIZE_CELLS_DEFAULT 1
 
 extern struct mutex of_mutex;
+extern raw_spinlock_t devtree_lock;
 extern struct list_head aliases_lookup;
 extern struct kset *of_kset;
 

include/linux/of.h

···
 #include <linux/errno.h>
 #include <linux/kobject.h>
 #include <linux/mod_devicetable.h>
-#include <linux/spinlock.h>
 #include <linux/topology.h>
 #include <linux/notifier.h>
 #include <linux/property.h>
···
 extern struct device_node *of_chosen;
 extern struct device_node *of_aliases;
 extern struct device_node *of_stdout;
-extern raw_spinlock_t devtree_lock;
 
 /*
  * struct device_node flag descriptions