powerpc/book3e-64: Wait til generic_calibrate_decr to enable decrementer

Match what we do on 32-bit Book-E processors and enable the decrementer
in generic_calibrate_decr.  We need to make sure we disable the
decrementer early in boot since we currently use lazy (soft) interrupt
on 64-bit Book-E and possible get a decrementer exception before we
are ready for it.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/exceptions-64e.S

@@ -774,9 +774,11 @@ _STATIC(init_thread_book3e)
 	/* Make sure interrupts are off */
 	wrteei	0
 
-	/* disable watchdog and FIT and enable DEC interrupts */
+	/* disable all timers and clear out status */
-	lis	r3,TCR_DIE@h
+	li	r3,0
 	mtspr	SPRN_TCR,r3
+	mfspr	r3,SPRN_TSR
+	mtspr	SPRN_TSR,r3
 
 	blr