ARM: imx: do not return from imx_cpu_die() call

When imx_cpu_die() is being called, the cpu should never return from the
call but just in WFI and wait for hardware to take it down.  So let's
do cpu_do_idle() repeatly in the call.  Doing this help improve the
relibility of hotplug operation.
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/mach-imx/hotplug.c

@@ -52,6 +52,8 @@ void imx_cpu_die(unsigned int cpu)
 	 * the register being cleared to kill the cpu.
 	 */
 	imx_set_cpu_arg(cpu, ~0);
+
+	while (1)
 		cpu_do_idle();
 }