sparc64: improve modularity tick options

This patch prepares the code for early boot time stamps by making it more
modular.

- init_tick_ops() to initialize struct sparc64_tick_ops
- new sparc64_tick_ops operation get_frequency() which returns a
  frequency

Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Reviewed-by: Bob Picco <bob.picco@oracle.com>
Reviewed-by: Steven Sistare <steven.sistare@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc/include/asm/timer_64.h

@@ -22,6 +22,8 @@ struct sparc64_tick_ops {
 
 	void (*init_tick)(void);
 	unsigned long (*add_tick)(unsigned long);
+	unsigned long (*get_frequency)(void);
+	unsigned long frequency;
 
 	char *name;
 };