Moving memory hotplug code from dlpar.c to memory-hotplug.c. This also moves
the hotplug elog struct to asm/rtas.h to make it accessible.

No functional changes.

Signed-off-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Migrate the cpu dlpar hotplug code to hotplug-cpu.c

No functional changes.

Signed-off-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>