powerpc: Fix early boot accounting of CPUs

smp_release_cpus() waits for all cpus (including the bootcpu) due to an
off-by-one count on boot_cpu_count (which is all CPUs).  This patch replaces
that with spinning_secondaries (which is all secondary CPUs).

Signed-off-by: Matt Evans <matt@ozlabs.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/head_64.S

@@ -255,7 +255,7 @@ generic_secondary_common_init:
 	mtctr	r23
 	bctrl
 
-3:	LOAD_REG_ADDR(r3, boot_cpu_count) /* Decrement boot_cpu_count */
+3:	LOAD_REG_ADDR(r3, spinning_secondaries) /* Decrement spinning_secondaries */
 	lwarx	r4,0,r3
 	subi	r4,r4,1
 	stwcx.	r4,0,r3