[MIPS] Sibyte: Fix race in sb1250_gettimeoffset().

From Dave Johnson <djohnson+linuxmips@sw.starentnetworks.com>:
    
sb1250_gettimeoffset() simply reads the current cpu 0 timer remaining
value, however once this counter reaches 0 and the interrupt is raised,
it immediately resets and begins to count down again.
    
If sb1250_gettimeoffset() is called on cpu 1 via do_gettimeofday() after
the timer has reset but prior to cpu 0 processing the interrupt and
taking write_seqlock() in timer_interrupt() it will return a full value
(or close to it) causing time to jump backwards 1ms. Once cpu 0 handles
the interrupt and timer_interrupt() gets far enough along it will jump
forward 1ms.
    
Fix this problem by implementing mips_hpt_*() on sb1250 using a spare
timer unrelated to the existing periodic interrupt timers. It runs at
1Mhz with a full 23bit counter.  This eliminated the custom
do_gettimeoffset() for sb1250 and allowed use of the generic
fixed_rate_gettimeoffset() using mips_hpt_*() and timerhi/timerlo.
    
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/sibyte/swarm/setup.c

@@ -70,6 +70,12 @@ const char *get_system_type(void)
 	return "SiByte " SIBYTE_BOARD_NAME;
 }
 
+void __init swarm_time_init(void)
+{
+	/* Setup HPT */
+	sb1250_hpt_setup();
+}
+
 void __init swarm_timer_setup(struct irqaction *irq)
 {
         /*
@@ -109,6 +115,7 @@ void __init plat_setup(void)
 
 	panic_timeout = 5;  /* For debug.  */
 
+	board_time_init = swarm_time_init;
 	board_timer_setup = swarm_timer_setup;
 	board_be_handler = swarm_be_handler;