powerpc: Fix event-scan code for 32-bit CHRP

On CHRP machines we are supposed to call into firmware (RTAS)
periodically, to give it a chance to check for errors and other
events.  Under ppc we had some special code in timer_interrupt
to do this, but that didn't get transferred over to arch/powerpc.
Instead, we use an array of timer_list structs, one per CPU,
and use add_timer_on to make sure each one gets called on the
appropriate CPU.

With this we can remove the heartbeat_* elements of the ppc_md
struct.

Signed-off-by: Paul Mackerras <paulus@samba.org>

include/asm-powerpc/machdep.h

@@ -176,10 +176,6 @@ struct machdep_calls {
 	   May be NULL. */
 	void		(*init)(void);
 
-	void		(*heartbeat)(void);
-	unsigned long	heartbeat_reset;
-	unsigned long	heartbeat_count;
-
 	void		(*setup_io_mappings)(void);
 
 	void		(*early_serial_map)(void);