ARM: imx: disable cpu in .cpu_kill hook

It's buggy to disable the cpu that is being hot-unplugged in .cpu_die
hook which runs on the cpu itself.  Instead, it should be done in
.cpu_kill which runs on the thread (another cpu) that asks for shutting
down the cpu.  Move imx_enable_cpu(cpu, false) call into .cpu_kill
hook, and leave the cpu to be hot-unplugged in WFI within .cpu_die,
so that we can get a more stable cpu hot-plug operation.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/mach-imx/platsmp.c

@@ -92,5 +92,6 @@ struct smp_operations  imx_smp_ops __initdata = {
 	.smp_boot_secondary	= imx_boot_secondary,
 #ifdef CONFIG_HOTPLUG_CPU
 	.cpu_die		= imx_cpu_die,
+	.cpu_kill		= imx_cpu_kill,
 #endif
 };