powerpc/smp: remove the incorrect decrementer initial codes for AP

We already defined start_cpu_decrementer() to invoke decrementer for AP as
the following path:

start_secondary() -> secondary_cpu_time_init() -> start_cpu_decrementer()

So remove these incorrect codes introduced from commit:
e7f75ad0 powerpc/47x: Base ppc476 support

And actually we really should not enable decrementer before calling set_dec().
Signed-off-by: NTiejun Chen <tiejun.chen@windriver.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/smp.c

@@ -499,14 +499,6 @@ int __devinit start_secondary(void *unused)
 	current->active_mm = &init_mm;
 
 	smp_store_cpu_info(cpu);
-
-#if defined(CONFIG_BOOKE) || defined(CONFIG_40x)
-	/* Clear any pending timer interrupts */
-	mtspr(SPRN_TSR, TSR_ENW | TSR_WIS | TSR_DIS | TSR_FIS);
-
-	/* Enable decrementer interrupt */
-	mtspr(SPRN_TCR, TCR_DIE);
-#endif
 	set_dec(tb_ticks_per_jiffy);
 	preempt_disable();
 	cpu_callin_map[cpu] = 1;