Currently, almost all architectures have switched to GENERIC_CPU_DEVICES,
except for arm32. Also switch over to GENERIC_CPU_DEVICES, and provide an
arch_register_cpu() that populates the hotpluggable flag for arm32.

The struct cpu in struct cpuinfo_arm is never used directly, remove
it to use the one GENERIC_CPU_DEVICES provides.

This also has the effect of moving the registration of CPUs from subsys to
driver core initialisation, prior to any initcalls running.
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>